THE MANIFOLD EFFECTS OF GENES AFFECTING FRUIT SIZE AND VEGETATIVE GROWTH IN THE RASPBERRY II. GENE I2 BY D. L. JENNINGS Scottish Horticultural Research Institute, Dundee {Received 16 September 1965)... SUMMARY Seedlings with 'miniature' fruits or with 'blind' fruiting laterals were found to segregate when thevaspberry varieties Norfolk Giant and Baumforth's Seedling B, were inbred. It was concluded that in each family both abnormalities were caused by the same recessive gene (/j), which had pleiotropic effects on each stage of growth. Its action was to decrease growth by amounts which increased progressively with each stage of the plant's development. The effects of the gene are compared and contrasted with those of gene Lj. INTRODUCTION The first paper of this series (Jennings, 1966) described the manifold effects of a gene which inhibited the development of raspberry canes in their first (vegetative) year, and considerably enhanced the growth of their fruiting laterals in the second season. The present paper compares and contrasts the effects of a gene which reduced the amount of growth produced by raspberries in both the first and second seasons of the cane's life. The study is mostly concerned with two families obtained by selfing the raspberry varieties Norfolk Giant and Baumforth's Seedling B. In both of these families a proportion of the seedlings had small fruits with exceedingly small drupelets; the fruits were otherwise well formed and hence they were described as 'miniatures'. The distinction between normal and miniature fruits was particularly clear in the Norfolk Giant family (Plate 8) and less so in the Baumforth family. In addition, both families contained a proportion of seedlings with 'blind' laterals which were completely free of fruits. When the families were recorded for a second season in 1961, many seedlings which were 'blind' in i960 were found to have 'miniature' fruits, and, conversely, many which had been recorded as having 'miniature' fruits in the previous year were found to be 'blind'. It appeared that these seedlings had a weakened capacity to produce fruits; sometimes they produced 'miniature' fruits, sometimes flower buds which failed to develop and were shed, and sometimes they failed to produce flower buds at all. Two further families obtained by crossing a 'miniature'-fruited seedling from each of the above-mentioned families with the variety Norfolk Giant were also studied. METHODS The methods of recording and subsequent treatment of the data were the same as those described in the first paper of this series (Jennings, 1966). 188
THE NEW PHYTOLOGIST, 6:;, 2 PLATE 8 Miniature (left) and normal (right) fruits from sister seedlings obtained by selfing the variety Norfolk Giant. D. L. JENNINGS G iy T/CS OF RASPBERRY. II (facing page i88)
Genetics of raspberry. II 189 RESULTS Segregation Details of the segregations obtained are given in Table i. 'Miniature'-fruited or 'blind' lateral types occurred in proportions which would be expected if this weakened capacity for fruit development were caused by the segregation of a single recessive gene. Table i. Segregation of forms of fruiting lateral in families related to the varieties Norfolk Giant and Baumforth's Seedling B Family Genotype X'^ 3: i P (a) selfed families Norfolk Giant Baumforth Seedling B Total 325 207 532 98 75 173 0.76 0.38 0.26 0.30-0.50 0.50-0.70 0.50 0.70 (b) Crosses between normal seedlings and seedlings with 'miniature' fruits N. Giant XS43/3* N. Giant XS35/15* Total 51 38 89 31 20 20 4.88 5.59 10.31 0.02-0,05 0.01-0.02 o.or * S43/3 and S35/15 are 'miniature'-fruited seedlings from the selfed families obtained from Norfolk Giant and Baumforth's Seedling B respectively. Table 2. Mean values for vegetative growth of Lj «"<^ h phenotypes in their first and second years after planting Family No. of canes Mean growth per cane (m) Cane diameter (mm) L2 I2 L2 I2 L2 I2 (a) First year after planting S43 (N. Giant) io.o 7.1 1.49 1.19 6.57 5.42 S35 (Baumforth B) 8.0 7.2 1.15 0.95 5.45 5.20 Mean 9.0 7.1 1.32 1.07 6.01 5.31 Variances Families 8.42 0.661 9.42 Genotypes 36.81 0.029 10.27 Within genotype 26.11 0.019 0.98 (b) Second year after planting S43 12.5 7.4 1.12 0.94 - S35 17.2 16.7 1.16 0.99 Mean 14.8 12.i 1.14 0.96 Variances* Families 1051.42 0.004 Genotypes 168.89 0.705 Within genotype 30.19 0.082 * Family or genotype variances are statistically significant (P = 0.05) if they are more than 1.35 times as great as the within-genotype variance. The designation Zj is used for the gene postulated, the normal phenotype being determined by Lj. For this hypothesis a 3 : i ratio of Lj : I2 forms would be expected for the selfed families and a i : i ratio for the crossbred ones. The x^-tests showed that the deficiency of recessive forms in the cross-bred families was statistically significant:
190 D. L. JENNINGS possibly these forms had a lower survival value. However the occurrence of 'miniature'- fruited forms in both of these families confirmed the hypothesis that the varieties Norfolk Giant and Baumforth's Seedling B are heterozygous at the same gene locus. Vegetative and lateral growth The effects of gene /j on cane and fruiting-lateral growth are shown in Tables 2 and 3. The inhibiting effect of the gene was shown by the numbers of canes produced, and by both the mean growth and diameters of the canes, though this was much more apparent in the family related to Norfolk Giant (S43) than in the one related to Baumforth's Seedling B (S35); the effect was not overcome when plant vigour became greater in the second year after planting. The main contrast with the action of gene L,, however. Table 3. Mean values for fruiting lateral growth of L2 and /^ phenotypes in their first year after planting Family S43 (N. Giant) S35 (Baumforth) Mean Variances* Families Genot>pes Within genotype Lateral diameter (mm) L2 h 3-69 3-44 3-33 3-60 3-51 3-52 0.208 0-043 0-596 Lateral length (cm) 24-32 16.22 16.92 14.35 20.62 15.29 451-69 598.67 38.28 * See footnote of Table 2. No. of lateral nodes L, h 11.32 9.22 9-54 9-35 10.43 9-29 14-35 27-44 8.37 was that gene I2 depressed lateral growth too. This is shown by reductions in the mean lateral lengths and mean numbers of lateral nodes present. As already mentioned, the flower number per lateral was considerably reduced, in some cases leading to the production of 'blind' laterals. Fruit size Data on fruit size are available only for the family obtained by inbreeding Norfolk Giant. They are given in Table 4. It is apparent that the //j seedlings had a much reduced seed size and hence drupelet size but there was only a small reduction in seed number Table 4. Mean values for fridt measurements 0/L2 phenotypes in family Weight ten fruits 19.0 + 0.50 8.5 ±0.80 43 No. seeds per fruit 78.7 + 1.41 65.7 + 3.35 84 Weight 100 seeds 0.9610.02 0.45+0.05 47 per fruit, which is indicative of the amount of reduction in drupelet number per fruit. This difference obviously gave the fruits their characteristic miniature appearance. DISCUSSION It seems probable that the manifold effects of gene I2 can be attributed, as suggested for gene Lj, to 'spurious' pleiotropism, that is to say, to the action of its product at each
Genetics of raspberry. II 191 stage of the plant's development. The main contrast between the actions of the two genes is that, apart from its effect on apical dominance, the inhibitory action of gene L^ was seen only on the diameters of the main stems; thereafter the gene increased growth by progressively increasing amounts. Gene /j, on the other hand, decreased the growth of each stage of development by amounts which increased with eaeh order of branching. For example, in the II2 genotypes of the Norfolk Giant family (S43) the mean vegetative growth of the cane apices was reduced to 80% of that in the L^ seedlings, the mean lateral growth was reduced to ()']% of the normals and the seed, which is strictly the ultimate branch, was reduced to 47% of the normal size. It was suggested that the action of gene L1 was to increase the concentration of a growth hormone in the plant to a level above the optimum for vegetative growth but advantageous for reproductive or lateral growth: in contrast it seems possible that gene I2 reduces the level of such a substance to one which is sub-optimal for all stages of development. REFERENCE JENNINGS, D. L. (1966). The manifold effects of genes affecting fruit size and vegetative growth in the raspberry. I. Gene Li. New Phytol., 65, 176.