THE GROWTH OF THE CHERRY OF ROBUSTA COFFEE L WEIGHT CHANGES CORRELATED WITH WATER AVAILABILITY DURING DEVELOPMENT BY J. DANCER Department of Agriculture, Kawanda Research Station, Kampala, Uganda {Received 26 April 1963) SUMMARY After a period of initial growth the water content of the cherry increases considerably although that of the bean is not high during early development. Leaf reduction early in the growth period or water deficit, early or late, reduces growth. The later increase in weight of the bean is due to an increase in dry matter. INTRODUCTION The coffee cherry, botanically a drupe, is composed of outer fleshy carpels and an inner endosperm the commercial bean. Exocarp and mesocarp form the so-called flesh of the cherry and this is separated from the endosperm by an endocarp the parchment of fermented, processed coffee. The endosperm is surrounded by a silver skin (the testa) which in this study has not been separated from the bean. The development of the cherry, from unfertilized ovary to maturity at picking time, takes about 10 months for the Robusta type of Coffea canephora in Uganda. Flowering of the samples taken for analyses took place in the second to third week of February in both years of the study and picking of the ripe cherry took place at the beginning of December. There is little or no reference to the growth and development of coflee cherries in the literature. However, comparable studies are being, or have been, undertaken for other developing seed organs. Eor example the study of the development of the ear of cereal grains (Archbold, 1945 ; Porter, Pal and Martin, 1950), peas (McKee, Robertson and Lee, 1955) and apple fruits (Robertson and Turner, 1951); the latter being the development of fleshy integuments. The growth of cereal grains and peas are most likely to bear some relation to that of the coffee cherry since the bean itself is composed of the fleshy cotyledonary leaves of the seedling. The object of the present observations was to study the growth in size of developing Robusta coflee cherry in relation to the availability of the calculated moisture supply. METHODS Sampling was undertaken at 20 day intervals from i April until 20 November in 1961. One primary was removed from each of four trees, designated A-D, and the number and 34
Development of the coffee cherry 35 weight of the berries from each node of the primary recorded. (A primary is an axillary growth or branch from the main stem which, when mature, bears flowers followed by the harvested cherry.) After removal of the cherries, the bean was dissected away from the outer flesh and this was also weighed. Dry weights of the whole cherry and the inner bean were obtained. On each sampling date about iooo berries were dissected. Sampling was discontinued before visible ripening processes commenced. In 1962 the experimental observations were extended to measure the influence of A.' /'^\ ' B/'/X:- 1-2- l-ou o 0-6- / ' ' / 5 0-Ac J 0-2- / / / 1 :/ / 2 n 1 April 20 10 May 20June 31 July 10 Sept. 20 Oct. Date of sampling Fig. I. Increase in mean fresh weight of cherries from four individual trees, A, B, C and D, 1961. lapril lomay 20June 31July losept. 200ct. Date of sampling Fig. 2. Mean fresh weight of cherry ( - ) and bean (x) together with dry weight of bean leaf number per primary on berry growth. Three adjacent trees were selected in each of three areas of a plantation. The primaries were selected on i March and all cherries other than those on the flrst seven nodes from the apex were removed. On subsequent counting this gave an average number per initial sample of some 2200 berries from nine trees. Sampling of the selected primaries commenced on 2 April, as previously, and continued at intervals of 25 days until 10 December. On 27 April the leaf pairs on the selected primaries of a selected tree in each group of three trees were
36 J. DANCER reduced to the three apical pairs. On 6 August a similar defoliation took place on a further selected tree in each group. Further leaf growth was not inhibited, in order to maintain three pairs of leaves per primary. All the cherries on a primary were counted and weighed when sampled. About a third of the cherries were weighed for dry weight determinations and a further third dissected to obtain fresh weight and dry weight of the flesh and bean. Dry weights of all samples were obtained by oven drying at ios"" C for 24 hours. Water deficits have been calculated from McCulloch's (1962) modifications to Penman's formula. : April 22 May 11 July 31 Aug. 19 Oct. 10 Dec. 2 April 22May luuly 31 Aug. 190ct. lodec. Date of sampling Fig. 3. (a) Mean fresh weight of cherries, (b) mean dry weight of cherries, (c) mean, fresh (A) and dry (B) weights of bean, and (d) percentage dr>' weight of cherr>' ( ) and bean ( ), in all cases of normal and defoliated plants. In (a) - (d), control ( ); defoliated on 27 April 1962 ( :-); defoliated on 6 August 1962 ( <). RESULTS The increase in fresh weight of the cherries of the individual trees in 1961 is shown in Fig. I, and Fig. 2 shows the mean increases in fresh weight of cherry and bean and also the dry weight of the bean. The increase in fresh weight of the cherry follows a sigmoid curve but that for fresh weight of the bean does not follow, proportionately, the curve for whole cherry. The dry matter content of the bean seems to increase most rapidly during the latter 2 months of formation. From the 1961 results, it appeared that leaf area per primary did not materially influence berry size but that genetic and/or environmental factors controlled absolute size
Development of the coffee cherry 37 at harvest. To investigate the influence of loss of leaf on berry growth, further additional observations on trees from which leaves were removed were undertaken in 1962. Fig- 3(^) indicates that leaf reduction in April had a marked effect on cherry growth but that in August it appeared to have little or no effect. The data for dry matter of cherry and fresh and dry weight of bean (Fig. 3(b) and (c)), confirm this conclusion. Fig. 3(d) shows the percentage dry matter of whole cherry and bean. It would appear that after the period of initial growth, the water content of the cherry increases considerably although that of the bean is not high during early development. The later increase in weight of the bean is due to increase in dry matter. The deficit in rainfall for three 10 day periods per month and the stored soil water occurring during the growing season is given in Table i. Reductions in growth-rate which occurred in 1961 during August and in 1962 during May and September, may be due to water deficits which occurred at these times. Table i. Water deficits {in.) as calculated from Penman s estimate (a) rainfall minus estimated evaporation; (b) stored soil water calculated by summing all the increments and deficits since i January each year. 1961 1962 (a) (b) (a) (b) April I +3-86 4.96 +2.80 0.50 2 +1.90 6.86 +1.16 +0.66 3 ~i-o5 5-8i 0.83 0.17 May I +0.77 6.58 0.19 0.36 2 0.67 5.91 013 0-49 3 o.i6 5.75 +0.65 +0.16 June I 2 +0.65 1.49 6.40 4.91 +0.54 1.16 +0.70 +0.46 3 +0.68 5.59 0.14 0.60 July I +0.07 5.66 +0.76 +0.16 2 0.65 5.01 +0.58 +0.74 3 "1-55 3-46 +0.86 +i.6o August I I.I I 2.3s +1.00 +2.60 2-1.27 1.08 +2.34 +4-94 3 +0.37 1.4s +0.84 +5-78 September i 0.96 0.49 i.ii +467 2-0.17 0.32-0.72 +3-95 3 +2.05 2.37 +0.58 +4-53 October i -0.84 1.53-1.09 +3-44 2 +1-43 2.96 +2.42 +5-86 3 +1.47 4-43 +3-67 +9-53 November i +4-29 +13-82 2 4-2.44 +16.26 3 +0.42 +16.68 DISCUSSION The results of McKee et a/. (1955) for seed development of pea fruits are similar to those observed for coffee cherry. Tt would appear that increase in fresh weight of both whole cherry and bean follows a sigmoid form in relation to time while the increase in dry matter is linear (Figs. 2, 3(b) and (c)). This is similar to the situation in the pea seed. The effect of restricting the photosynthetic area of a primary during early development of the cherry is to reduce the final weight of the cherry and bean by about 30%. If, however, defoliation takes place later in relation to cherry development no reduction in size is apparent. After this late defoliation relatively little increase in the fresh weight of the cherry or the bean occurs although the increase in dry matter is considerable and
38 J. DANCER most rapid. It would appear, therefore, that reduction in leaf area during the maturation of the cherry is not as important to the growth of the cherry as that which may occur during early development. It may be that the developing berrv obtains the required metabolites from reserves re-utilized from other portions of the tree in the process of accumulation of dry matter. The contribution of photosynthates by the cherry itself is a further factor complicating the analysis of growth. It may be that when increase in fresh weight is complete, photosynthates in the cherry can supply enough metabolites for maturation, and thus defoliation would not hinder development at this stage. Should defoliation take place earlier in development, when insufficient metabolites have been formed by the cherry to further its own growth, then defoliation may have a retarding effect on development. Both Archbold (1945) and Porter et al. (1950) studying the growth of barley have shown that the ear photosynthesizes a considerable quantity of metabolites during its own growth and it would be reasonable to assume that this was also true of the coffee cherry. The influence of moisture deficits in retarding the grovi^th of crops is well known. There appears to be a reduction of the growth-rate in the cherry of Robusta coffee when water deficits occur although further investigation is necessary, and is at present being undertaken, to determine if water applications can increase cherry size. ACKNOWLEDGMENTS Permission to publish this communication from the Director of Agriculture, Uganda, is acknowledged. REFERENCES ARCHBOLD, H. K. (1945). Some factors concerned in the process of starch storage in the barley grain. Nature, Lond., 156, 70. McCuLLOGH, J. S. G. (1962). Tables for the Rapid Computation of the Penman Estimate of Evaporation. E.A.A.F.R.O., Mugaga, Kenya. MCKEE, H. S., ROBERTSON, R. N. & LEE, J. B. (1955)- Physiology of pea fruits, i. The developing fruit. Aust.y. biol. Sci., 8, 137. PORTER, H. K., PAL, N. & MARTIN, R. V. (1950). Physiological studies in plant nutrition. XV. Assimilation of carbon by the ear of barley and its relation to the accumulation of dry matter in the grain. Ann. Bo/., Lo?!<i., N.s., 14, 55. ROBERTSON, R. N & TURNER, J. F. (1961). The physiology of gro^vth in apple fruits. 11. Respiratory and other metabolic activities as functions of cell number and cell size in fruit development Aust J sci Res., B, 4, 92.