THE GENETICAL CONTROL OF THE EVERBEARING HABIT AND THREE OTHER CHARACTERS IN VARIETIES OF FRAGARIA VESCA

Transcription

1 Euphytica 14 (1965): THE GENETICAL CONTROL OF THE EVERBEARING HABIT AND THREE OTHER CHARACTERS IN VARIETIES OF FRAGARIA VESCA T. BROWN* and P. F. WAREING** Botany Department, University of Manchester, Manchester, England With 9 figures Received 31 Aug. I964 A genetical study was made of three diploid varieties of Fragaria vesca, namely, wild type and two cultivated Alpine varieties, "Baron Solemacher" and "Bush White". The varieties differ in several characters, including flowering habit, runnering habit, branching habit and fruit colour. Wild type is seasonal flowering, produces runners, has a simple branching habit and has red fruit. Both the Alpine varieties have a perpetual flowering (everbearing) habit and produce no runners. "Baron Solemacher" resembles wild type in branching habit and fruit colour, whereas "Bush White" has a very bushy habit (i.e., has a large number of crowns per plant) and has white fruit. Wild type F. vesca was crossed with the two Alpine varieties, and the F, progenies were selfed and back-crossed to the Alpine parents. The results indicate that the differences in flowering habit are controlled by a single major gene, seasonal flowering being dominant to perpetual flowering, the recessive alleles in the two perpetual flowering varieties apparently being identical. Differences in runnering habit also appear to involve a single gene locus but non-runnering is associated with the bushy habit in "Bush White" and therefore either the three alleles of the same gene occur or the gene controlling bushiness in separate but closely linked with the gene controlling runnering. Fruit colour is controlled by one major gene locus, red being dominant to white fruit. All three major genes segregate independently. In all cases the characters of the wild type are dominant. The possible nature of the physiological process controlled by the gene for flowering habit is discussed. It is well-known that in cultivated strawberries there are two distinct habits of flowering duration, seasonal flowering and perpetual flowering (everbearing). Most of the popular varieties of strawberry grown in Europe are seasonal flowering, i.e. they flower in spring and produce fruit in midsummer. Other varieties, however, which have the everbearing habit, continue to produce flowers and fruit through spring, summer and autumn. The first fruits are formed as soon as the first emerging flowers in spring develop and fruiting continues until conditions are no longer favourable for growth in autumn. Genetical studies have been carried out on the flowering habit in American straw- * Present address: Geology Department, University, Sheffield. ** Present address: Botany Department, University College of Wales, Aberystwyth, Wales. 97

2 T. BROWN AND P. F. WAREING berries by CLARK (1937), DARROW (1937) and POWERS (1954). Several cultivated varieties were studied, also the wild Rocky Mountain species Fragaria ovalis (POWERS, 1954). In all cases the inheritance of the flowering habit appeared complex; usually the seasonal flowering habit was dominant but in some cases the everbearing habit was dominant. In no case could the type of inheritance be attributed to a single gene effect. The American cultivated everbearing strawberries differ in origin from the European everbearing cultigens (DARROW, 1937 ; LE SOURD, 1944; RICHARDSON, 1914) and their everbearing habit is probably controlled by a different gene complex. In the European cultivated everbearing strawberries, however, again the genetical control appears to be complex and no single gene appears to control the everbearing habit (RICHARDSON, 1914). The complexity of the genetical control in most cultivated varieties is probably largely due to their polyploid nature. Cultivated strawberries are mainly octoploid (2n = 56) and appear to have originated from hybrids between F. virginiana and F. chiloensis (LE SOURD, 1944). The European "Alpine" strawberries are naturally-occurring everbearing forms of F. vesca and are diploid (2n = 14). It is thought that the European everbearing strawberries originated by crosses made by the AbbC THIVOLET between "Alpine" everbearing strawberries and seasonal flowering cultivated polyploid varieties, a very difficult cross to make (LE SOURD, 1944; RICHARDSON, 1914). Therefore, although the everbearing habit is difficult to study in most of the cultivated varieties because of the polyploidy, a clue to the type of genetical control may be obtained by a study of the everbearing habit of diploid Alpine varieties. Many of the Alpine varieties produce no runners. This interesting character was also thought worthy of investigation since no conclusive work has been done to find the genetical control of this character, although it has previously shown that runnering is dominant to non-runnering in F. vesca (RICHARDSON, 1923 ; NIL~SON and JOHANSSON, 1944). Also it was of interest to see to what extent this character was related to the everbearing habit, since seasonal flowering strawberries tend to produce runners only in the vegetative phase of development. Alpine cultigens are varieties of the wild strawberry Fragaria vesca. The wild type of F. vesca produces runners and has a seasonal flowering habit. The present paper describes a study of the mode of inheritance of the everbearing - seasonal flowering habits and runnering - non-runnering habits in varieties of F. vesca. One of the Alpine varieties, "Bush White", also produces white fruit and has a very bushy habit. A study of the inheritance of these characters was included. Three varieties of F. vesca were used, namely a wild strain and the two Alpine cultigens, "Baron Solemacher" and "Bush White" (Fig. 1). Wild Type Wild F. vesca shows two fairly distinct phases of development. After flowering in spring it enters a phase of vegetative growth which continues until autumn when flower primordia are initiated which emerge in the following spring. In the vegetative state F. vesca consists of a thick stem with short internodes, refer- 98

3 GENETICAL STUDY OF FRAGARIA VESCA FIG. 1. Typical plants of wild type Fragaria vesca and the Alpine varieties "Bush White" and "Baron Solemacher". red to as a "crown". Primordia, which are formed in the axils of leaves in the apical region, develop either into runners or into buds which are potential lateral crowns. During the vegetative phase of growth almost every axillary develops into a runner. The difference between buds and runners can be seen at a very early stage in the development since in a bud primordium all the internodes remain short, while in a runner primordium the first internode very soon elongates. When the runner emerges from the crown the first two internodes elongate and subsequent internodes are short, thus forming the new crown of the offset. WILD TYPE SEASONAL -FLOWERING RUNNERING FIG. 2. Pattern of development of wild F: vesca :: KEY TERMINAL INFLORES- CENCE -VEGETATIVE APEX INTERNODE LEAFIVEGETATIVE BUD LEAF+FLOWERING BUD RUNNER

4 T. BROWN AND P. F. WAREING In late summer the rate of runner production falls and lateral buds are initiated instead of runners. When the flowering phase is entered in autumn, the terminal apex becomes an intlorescence and the growth of the main crown is continued by the topmost axillary bud. Usually several axillary buds near the apex grow out at this time, producing lateral crowns. Some of these lateral crowns may also develop apical inflorescences and in each case the growth of the crown is continued by the topmost axillary bud. Once the new lateral crowns are established they grow as independent units, following a pattern of development similar to that described for the main crown. The development of a plant of wild F. vesca, up to the onset of flowering, is represented diagramatically in Fig. 2. A number of plants was examined and the example shown in Fig. 2 was typical. The diagram was constructed from the dissection of a well-established crown of F. vesca. Axillary buds remain alive, protected by the shrivelled leaf bases, long after the subtending leaves have died. The bases of old runners also remain intact, protected by the leaf bases. The growth throughout a complete season or longer can therefore be recorded by dissecting an old crown. GUTTRIDGE (1955) had described the development of several cultivated varieties which are seasonal -flowering and produce runners and in many respects their development is similar to that of F. vesca. "Baron Solemacher" The Alpine variety "Baron Solemacher" differs from wild type in that it produces no runners and has a perpetual flowering habit. Its origin is described by GOETZ (1935). Comparing "Baron Solemacher" with wild type (Figs. 2 and 3), it can be seen that BARON SOLEMACHER PERPETUAL FLOWERING NON-RUNNERING b P LEAFIFLOWERING KEY TERMINAL INFLO- RESCENCE --VEGETATIVE APEX INTERNODE LEAFtVEGETATIVE BUD BUD FIG. 3. Pattern of development of "Baron Solemacher"

5 GENETICAL STUDY OF FRAGARIA VESCA after producing a few nodes the apex becomes an inflorescence and, as in the wild type, growth is continued by the axillary bud of the leaf immediately below the inflorescence. This lateral shoot develops only two or three leaf primordia before its apex becomes an inflorescence, and growth is continued by the topmost axillary bud. Development continues in this way throughout the growing season. The axillary buds formed usually remain dormant, although frequently the apex differentiates into a primordial inflorescence. Occasionally one of the axillary buds grows out to form a new lateral crown. The frequency with which new crowns arise in "Baron Solemacher" appears to be controlled mainly by the nutritional status of the plant and it is comparable with the frequency of lateral crown production in wild type F. vesca in a flowering condition. In "Baron Solemacher" there is a complete absence of runners; all the axillaries either remain dormant as buds or grow out as new lateral crowns. "Bush White" The other Alpine variety used was "Bush White" which, like "Baron Solemacher', produces no runners and has a perpetual flowering habit. "Bush White" differs from both wild type and "Baron Solemacher" in that it has white fruit and has a very bushy habit. The bushy habit is due to the development of a very large number of small crowns, instead of only few a large crowns as in wild type and "Baron Solemacher". The general pattern of development (Fig. 4) is similar to that of "Baron Solemacher" in that the apex becomes an inflorescence after producing only two or three nodes, growth of the crown being continued by the topmost axillary which itself becomes an BUSH WHITE PERPETUAL FLOWERING NON TERMINAL INFLO- RESCENCE FIG. 4. Pattern of development of "Bush White" LEAF+VEGETATIVE BUD LEAFIFLOWERING BUD

6 T. BROWN AND P. F. WAREING inflorescence after producing two or three nodes. Development continues in this way throughout the growing season. The difference in branching habit arises because in "Bush White" most of the lateral buds grow out to form new crowns which become further sub-divided, whereas in "Baron Solemacher" most of the lateral buds remain dormant even though they produce flower primordia, and only two or three form new crowns. There appears to be a lack of apical dominance in "Bush White" as compared with "Baron Solemacher" and wild type, apical dominance being greatest in wild type in a vegetative state. The plant shown as a diagram in Fig. 4 was only a young plant; crown production continues in this way and a plant in its second season may have up to fifty crowns. A summary of the character of the parent varieties is given in Table 1. TABLE 1. THE CHARACTERS OF THE PARENT VARIETIES Character Wild type Baron Solemacher Bush White Flowering habit seasonal perpetual perpetual Runnering habit runnering non-runnering non-runnering Branching habit simple simple bushy Fruit colour red red white A single clone of each of the parent types was used. The clones of "Baron Solemacher" and "Bush White" were of commercial origin and the clone of wild type was built up from a single wild plant of F. vesca from Wydale, Yorkshire. All three parent varieties were selfed for three generations and they bred true for all the characters shown in Table 1. Detailed observations of other characters were not made, but there was no obvious deviation of the progeny from the parent types. The genetical control of the four characters was investigated by crossing wild type F. vesca with both of the Alpine varieties "Baron Solemacher" and "Bush White". Observations were made on the F, plants, then these were selfed and back-crossed with the Alpine parent. The resulting F, and backcross progeny were used to record segregation for the four characters given in Table 1. Usual precautions were taken to prevent contamination by foreign pollen. All instruments and the hands of the operator were sterilized with absolute alcohol before each cross was made. Flowers to be used for pollen were gathered before the anthers opened and were allowed to dehisce in sterile petri dishes. Flower buds were used as female parents just before the calyx opened. Calyx, corolla, and rtndroecium were removed and after pollination the receptacle was enclosed in a gelatine capsule plugged with cotton wool. To effect selfing, complete flower buds were enclosed in gelatine capsules plugged with cotton wool before the calyx opened. Seeds were sown in seed pans in John Innes seed compost and the seedlings were potted on into John Innes No. 1 compost when $3 inches tall, care being taken not to leave unpotted any of the smaller, slow-germinating seedlings.

7 GENETICAL STUDY OF FRAGARIA VESCA From the time of sowing in autumn, the F,-plants were maintained under long-day conditions in daylight supplemented by illumination from tungsten filament lamps and mercury vapour lamps to give 18-hour photoperiods; under these conditions the wild type produced runners and remained vegetative (p. 110). The temperature was maintained above 60 F as far as possible to permit the distinction of seasonal and perpetual flowering plants (p. 1 lo), but efficient heating was not available during the development of the F,-progeny and the temperature occasionally fell to 50-55"F, which resulted in their flowering (see below). RESULTS Crosses of wild type with "Baron Solemacher" and "Bush White" Crosses were made using clonal plants of wild type as female, and clonal plants of the Alpine varieties as male parents. Five crosses were made in each case. Seeds from four fruits of the cross wild type x "Baron Solemacher" were sown yielding 33 F, seedlings, and seeds from two fruits of the cross wild type x "Bush White" yielded 31 F, seedlings. Throughout the period of observation the F, plants were kept in long photoperiods under the conditions given above. The seeds were sown in August and observations were made at monthly intervals on the runnering and flowering behaviour. The F, seedlings of both crosses remained vegetative throughout the winter, producing runners freely. Seedlings of the Alpine parents selfed, grown under the same conditions and at the same time, produced flowers at a very early stage in development. In the following April and May all the F, seedlings showed a marked reduction in runner production and developed inflorescences, probably in response to a fall in greenhouse temperature (see p. 110). Seedlings of wild type F. vesca grown at the same time in the same greenhouse also produced flowers at this time. Observations were continued and it was seen that F, plants of both crosses and wild type seedlings discontinued flowering after a time and entered a vegetative phase of development with runner production. Seedlings of the selfed Alpines, however, continued to flower. Thus it was observed that all 33 F, seedlings of wild type x "Baron Solemacher" and all 31 F, seedlings of wild type x "Bush White" were similar to wild type in all the observed characters; i.e., they were seasonal flowering, produced runners, were simple branched and had red fruit. These characters thus appeared to be dominant. F, and back-cross progeny In order to investigate the control of the four characters further, F, plants were selfed and back-crossed to the respective Alpine parents, using the F, hybrids as female and the Alpines as male parents. The seeds were sown and the seedlings were grown under long-days at temperatures above 60 OF. Segregations for the four characters were recorded. The following numbers of seedlings were grown and kept under observation: F, (wild type x "Baron Solemacher") = 81 plants (from 3 fruits) Back-cross (wild type x "Baron Solemacher") x "Baron Solemacher" = 150 plants (from 3 fruits)

8 A%- - - T. BROWN AND P. F. WAREING F, (wild type x "Bush White") = 143 plants (from %fruits) Back-cross (wild type x "Bush White") x "Bush White" = 164 plants (from 3 fruits) More seedlings were obtained from other fruits of the F2 and back-cross of wild type x "Bush White" but these were kept outside and were only used for observations on fruit colour. Segregation of characters in the F2 andfirst back-cross progeny (a) Segregation for runnering andjowering habits The runnering and flowering behaviour of the F, and back-cross progeny was recorded at monthly intervals over a period of ten months. Some of the seedlings started to produce runners or inflorescences at a very early stage of development but it was necessary to continue observations over several months because runnering tended to be erratic when associated with the perpetual flowering habit and several plants first recorded as perpetual floweringlnon-runnering later produced runners. The plants segregated into all four possible types. In addition to the parent types seasonal flowering/runnering and perpetual floweringlnon-runnering - I The results are shown in Table 2 and Figs. 5 and 6. the two new types arose, i.e. seasonal flowering/non-runnering and perpetual floweringlrunnering. The numbers obtained agree very well with those expected on a 9 : 3 : 3 : 1 segregation in the F2 progeny and with a 1 : 1 : 1 : 1 segregation in the back-cross progeny. TABLE 2. SEGREGATION A. Wild type x "Baron Solemacher" IN THE Fa AND BACK-CROSS PROGENIES Back-cross or Self Seasonal Seasonal Perpetual Perpetual flowering flowering flowering flowering P. Runnering Non-runnering Runnering Non-runnering Selfed < 0.7 Expected > 0.5 Backcrossed to < 0.7 Baron Solernacher Expected > 0.5 B. Wild type x "Bush White" Back-cross or Self Seasonal Seasonal Perpetual Perpetual flowering flowering flowering flowering P. Runnering Non-runnering Runnering Non-runnering Selfed Expected < 0.5 > 0.3 Back-crossed to "Bush White" Expected

9 GENETICAL STUDY OF FRAGARIA VESCA FIG. 5. The four phenotypes of the F, progeny of the cross wild type x "Baron Solemacher" FIG. 6. The four phenotypes of the F, progeny of the cross wild type x "Bush White" This suggests that in each case wild type differs from the Alpine variety by two mzjor genes. One gene controls runnering habit (R, r) with runnering (R) dominant to nonrunnering (r), and the other gene controls flowering habit (S, s) with seasonal flowering (S) dominant to perpetual flowering (s). The two genes segregate independently to produce the ratios observed in the F, and back-crosss progenies. (b) Segregation for fruit colour "Bush White" differs from both "Baron Solemacher" and wild type in fruit colour. The F, progeny of wild type x "Bush White" all had red fruit as in wild type. Segregation for fruit colour was observed in 173 F, progeny and in 157 back cross progeny giving the following results: F2 130 red fruited plants: 43 white fruited plants F, back-crossed to "Bush White" 72 red fruited plants: 85 white fruited plants

10 T. BROWN AND P. F. WAREING These results agree very well with 3 : 1 and 1 : 1 ratios respectively. It appears therefore that the difference in fruit colour between wild type and "Bush White" is also controlled by a single major gene with red (C) dominant to white (c). This conclusion agrees with the results of RICHARDSON (1914, 1923) for F. vesca. Segregation for fruit colour was independent of both of the two major genes controlling runnering and flowering habits. The segregations obtained for all three characters, presented in Table 3, do not differ significantly from ratios expected from independent segregation of the three genes. TABLE 3. SEGREGATION FOR FRUIT COLOUR, FLOWERING HABIT AND RUNNERING, IN F2 AND BACK-CROSS PROGENY OF WILD TYPE x "BUSH WHITE" Seasonal Seasonal Perpetual Perpetual Fruit Colour flowering flowering flowering flowering P Runnering Non-runnering Runnering Non-runnering Red Fruit Expected < 0.2 White fruit > 0.1 Expected Back-cross to "Bush White" Seasonal Seasonal Perpetual Perpetual Fruit Colour flowering flowering flowering flowering P. Runnering Non-runnering Runnering Non-runnering Red fruit Expected < 0.7 White fruit > 0.5 Expected (c) Branching habit "Bush White" has a very bushy habit in contrast to the simple branching habit of both wild type and "Baron Solemacher". It was found that the most satisfactory method of assessing the degree of "bushiness" was by counting the number of crowns of plants of a similar age. Crown numbers were therefore recorded on the F, and back-cross plants of wild type x "Bush White". The back-cross plants of wild type x "Baron Solemacher" were also scored for comparison of a type with a simple branching habit. At the time the crowns were counted the seasonal flowering plants were flowering. In seasonal-flowering, simple-branched plants t4e onset of flowering is accompanied by an increase in crown number from one or two in the vegetative state to 4-12 crowns when flowers are initiated. It was observed that bushiness tended to be associated with non-runnering, therefore the plants were grouped according to their flowering and runnering habits, and crown numbers were recorded within each group.

11 GENETICAL STUDY OF FRAGARIA VESCA 20- BARON SOLEMACHER X WlLD TYgE SEASONAL FLOWERING RUNNERING," z BACK-CROSSED SEASONAL FLOWERING NON-RUNNERING 10- NO. OF CROWNS/PLANT PERPETUAL FLOWERING RUNNERING "1 PERPETUAL FLOWERING NON-RUNNERING FIG. 7. Crown numbers of the back-cross progeny (Wild-type,: Baron Solemacher) x Baron Solemacher The results are expressed as histograms in Fig. 7, 8 and 9. The back-cross plants of wild type x "Baron Solemacher", which can be taken as typical examples of simplebranched plants in a flowering state, had up to 12 crowns per plant whether they were runnering or non-runnering (Fig. 7). BUSH WHITE X WlLD TYPE 201 SEASONAL FLOWERlNG "1 2 Is- Z 4 a 10- LL 9 a '1 RUNNERING PERPETUAL FLOWERING RUNNERING 15' BACK-CROSSED SEASONAL FLOWERING NON-RUNNERING No OF CROWNSlPLANT PERPETUAL FLOWERING NON-RUNNERING FIG. 8. Crown numbers of back-cross progeny, (Wild-type X Bush White) X Bush White.

12 201 T. BROWN AND P. F. WAREING BUSH WHITE X WILD TYPE SELFED SEASONAL FLOWERING 201 SEASONAL FLOWERING RUNNERING NON-RUNNERING z 4 a LL 0 d z NO. OF CROWNSIPLANT I I I a PERPETUAL FLOWERING RUNNERING 10 PERPETUAL FLOWERING NON-RUNNERING FIG. 9. Crown numbers of the F, progeny of Bush White x Wild-type. The histograms for the F, and back-cross plants of wild type x "Bush White" show that in this case runnering was associated with low crown numbers (Figs. 8, 9). All the runnering plants, both seasonal and perpetual flowering have low crown numbers and they have a simple branching habit. All the non-runnering plants (with two exceptions) have a bushy habit with crown numbers from 14 to 46 per plant. In perpetual-flowering plants the runnering character tends to be delayed and infrequent in expression and many of the plants included in the group, perpetual floweringlrunnering, did not produce any runners until the second season of growth. These were classed as runnering. Thus the two perpetual flowering non-runnering F, plants with exceptionally low crown number for this group, i.e. 7 and 12, may have been genotypically runnering. From the above results it can be seen that in "Bush White" the non-runnering habit is associated with a bushy branching habit. This suggests that the recessive gene controlling the non-runnering habit of "Bush White" also controls the bushy habit, or that the two characters are controlled by closely linked genes and the two exceptional plants arose by a cross-over between the two genes. The conclusions to be drawn from the results given above are that wild type F. vesca differs from the Alpine variety "Baron Solemacher" at two major gene loci, one controlling flowering habit and the other controlling runnering habit; the two genes segregate independently. Wild type F. vesca also di&rs from the Alpine variety "Bush White?' at three major gene loci, controlling flowering habit, runnering habit and fruit colour and all three genes segregate independently. The bushy habit of "Bush White" is closely associated with the non-runnering habit.

13 GENETICAL STUDY OF FRAGARIA VESCA Flowering habit. The difference in flowering habit between wild type and the two Alpine varieties is in each case controlled by a single major gene (Ss) with seasonal flowering (S) dominant over perpetual flowering (s). In another series of breeding experiments (BROWN, 1956) "Baron Solemacher" and "Bush White" were interbred as far as F, and double back-cross progeny. In all cases the perpetual flowering habit was constant. This suggests that the perpetual flowering habit is in both cases controlled at the same locus and probably by the same allele. Although the origin of "Baron Solemacher" is known (p. loo), the authors have been unable to trace any information regarding the origin of "Bush White". It seems very probable, however, that both varieties are derived from the naturally-occurring perpetual flowering Alpine forms of F. vesca. Since all parent types bred true on selfing, the genotypes for flowering habit can be expressed as follows : wild type - SS - seasonal flowering "~aron Solemacher" ss - perpetual flowering "Bush White" -1 - Runnering habit. It seemed possible, before the breeding programme was carried out, that runnering may be directly associated with flowering habit. Seasonal flowering wild type F. vesca ceases runner production when flowering; therefore "Baron Solemacher" and "Bush White" might not produce runners simply because they are perpetual flowering. The results given above disprove this. It was seen that in the F, and back-cross progeny of wild type with the two "Alpine" varieties, the perpetual flowering habit reduced the frequency of runner production but it could not completely supress it. Runnering habit was found to be controlled by another major gene which was not linked with the major gene controlling flowering habit. In each case wild type has the dominant allele (R) for runnering and both "Baron Solemacher" and "Bush White" have the recessive allele (r). The experiments described in the present paper do not show that the recessive allele of the Alpine varieties was the same in both cases or even that they occurred at the same locus. The other series of crosses discussed above, between the two Alpine varieties, suggested that the control of runnering is more complex than the control of flowering habit. The two Alpine varieties appeared to have recessive alleles for non-runnering at the same gene locus but in "Bush White" the situation is complicated by the fact that the non-runnering habit is closely associated with the bushy habit. The situation was further complicated by other genetic effects (probably additive minor genes) which were able to produce runnering in the absence of the dominant allele (R) of wild type (BROWN, 1956). Fruit colour. It was shown that the difference in fruit colour between wild type and "Bush White" is controlled by a single major gene, the segregation of which is independent of the genes controlling runnering and flowering habits. F, and other progeny of crosses between wild type and "Baron Solemacher" showed no variation in fruit colour, therefore it is probable that both wild type and "Baron Solemacher" have the same dominant allele for fruit colour.

14 T. BROWN AND P. F. WAREING The genotypes of the three parent varieties with regard to fruit colour are therefore: wild type "Baron Solemacher" "Bush White" - CC - red fruit - cc - white fruit Bushy habit. The results indicated that in "Bush White" the bushiness and the nonrunnering habit are so closely associated that they must be controlled either by the same allele or by closely linked genes. The gene constitutions of the parent types controlling the runnering and branching habits are therefore : either wild type - RR - runnering "Baron Solemacher" - rr - non-runnering "Bush White" - rbrb - non-runnering and bushy or wild type - RB RB - runnering; simple branched "Baron Solemacher" - rb rb - non-runnering; simple branched "Bush White" - rb rb - non-runnering; bushy Physiological signijicance It is interesting to consider the type of physiological reaction controlled by the gene affecting flowering habit. The environmental conditions controlling flowering and runnering have been studied in detail for octoploid cultivated strawberries by several workers. It was found that at temperatures above 15 "C, flower initiation is controlled by photoperiod and occurs only under short-day conditions; at temperatures below 15"C, flowering will occur under both short-day and long-day conditions (DARROW and WALDO, 1934; VAN DEN MUIJZENBERG, 1942 ; HARTMAN, 1947 ; WENT, 1952). Runnering is promoted by long-days and high temperatures (20 C-25 C). There appear to have been no previous physiological studies on the flowering and runnering of the wild-type seasonal flowering F. vesca, but perpetual flowering varieties of this species have been studied by SIRONVAL (1950) who found that such varieties continued to flower under both long- and short-days, and showed only quantitative differences in response to photoperiod and temperature. Thus, the physiological state necessary for flower initiation arises spontaneously in the perpetual flowering plants whereas it has to be induced by specific environmental conditions in the seasonal flowering plants. Experimental evidence (BROWN, 1956) showed that flower initiation can be induced in wild type F. vesca only within the narrow temperature range 50"-60 F; it was found that at 45 F and above 60 F flower initiation could not be induced under either long days or short days. Within the narrow temperature range 50"-60 F flower initiation was accelerated by short photoperiods but it was not inhibited by long photoperiods, only delayed by three to four weeks. It was found by defoliation experiments that the apex itself received the stimulus and reacts to inductive temperatures. It was also found that a minimum induction period of 4-5 weeks at the required temperature range was necessary to initiate flowers. It was concluded that in its natural environment wild type

15 GENETICAL STUDY OF FRAGARIA VESCA F. vesca initiates flowers in autumn in response to a continuous period of cooler temperatures within the required temperature range. It was found that runnering occurred continuously under long days, as had been established for octoploid cultivated varieties. It is evident that the dominant gene for seasonal flowering gives rise to a requirement for cool temperatures (50"-60 F) for flower initiation. The recessive gene for perpetual flowering introduces a lack of this requirement. The mutation of a dominant gene in wild type to a recessive allele usually occurs by the loss of an enzyme-controlled reaction, not by the introduction of an entirely new reaction. It appears, therefore, that flowering in F. vesca may be controlled by a balance of promoting and inhibitory processes. Above 60 F the inhibitory processes prevent flower initiation and below this temperature insufficient inhibitor is produced to prevent flowering. The flower promoting process apparently has a lower temperature coefficient than the inhibitor and induction of flowering is prevented only by temperatures lower than 50 F. It is of interest to note that GUTTRIDGE (1959, a, b) has obtained evidence for the occurrence of a flower-inhibiting substance in strawberries which is produced under long-days. Thus, the mutation from seasonal flowering to perpetual flowering may result in the loss of the ability to produce the flower inhibitor. The work described in this paper was carried out at the Botany Department, University of Manchester and the authors wish to express their thanks to Professor S. C. HARLAND, F.R.S., for suggesting this investigation and for providing facilities. The work was carried out during the tenure by one of us (T.B.) of a research studentship awarded by the Agricultural Research Council. REFERENCES 1. BROWN, T., Genetical and physiological aspects of flower initiation and runner production in varieties of Fragaria vesca L. Ph. D. Thesis, University of Manchester. 2. CLARKE, J. H., Inheritance of the so-called everbearing tendency in the strawberry. Proc. Amer. Soc. Hort. Sci. 35: DARROW, G. M. and WALDO, G. F., Responses of strawberry varieties and species to duration of the daily light period. U.S. Dept. Agr. Tech. Bull DARROW, G. M., Strawberry Improvement. Yearbook of Agriculture. United States Department of Agriculture GOETZ, O., Die rankenlose, immertragende Monatserdbeere "Baron Solemacher". Obst- u. Gemiiseb. 81 : GUTTRIDGE, C. G., Observations on shoot growth of cultivated strawberry plants. Jour. Hort. Sci. 30: GUTTRIDGE, C. G., 1959a. Evidence for a flower inhibitor and vegetative growth promoter in the strawberry. Ann. Bot. 23: , 1959b. Further evidence for a growth promoting and flower inhibiting hormone in strawberry. Ann. Bot. 23: HARTMANN, H. T., 1947b. Some effects of temperature and photoperiod on flower formation and runner production in the strawberry. Plant Physiol. 22: LE SOURD, F., Le Fraisier. New edition revised by Ch-A Simmer, Paris. 11. MUIIZENBERG, E. W. B. VAN DEN, De invloed van licht en temperatuur op de periodieke ontwikkeling van de aardbei (Fragaria grandiflora EHRH.) en de betekenis daarvan voor de teelt. Meded. Lab. voor Tuinbouwplantenteelt Wageningen 37: NILSSON, F. and JOHANSSON, E., Nya typer och hybrider inom slaktet Fragaria (New types and hybrids in the genus Fragaria). Sverig. Pomol. Foren. Arsskr. 45; Plant Breeding Abstracts (1947) 17:

16 T. BROWN AND P. F. WAREING 13. POWERS, L., Inheritance of period of blooming in progenies of strawberries. Proc. Amer. Soc. Hort. Sci. 64: RICHARDSON, C. W., A preliminary note on the genetics of Fragaria. Jour. Genet. 3: RICHARDSON, C. W., Notes on Fragaria. Jour. Genet. 10: SIRONVAL, C., Recherches organographiques et physiologiques sur le dkveloppement du fraisier des quatre-saisons B fruits rouges. Archiv. de L'Inst. de Bot. 20, No. 3: WENT, F. W., The experimental control of plant growth. Chronica Botanica 17,343 pp.