Ellis, RH

Osei-Bonsu, K

Roberts, EH

English

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Effect of time of harvesting on the storability of chickpea (Cicer arietinum L.) seeds K. OSEI-BONSU, R. H. ELLIS & E. H. ROBERTS (K. o.-B. & R.H.£.: Cocoa Research institute, P. 0. Box 8, Tajo-Akim, Ghana; E. H. R.: Department of Agriculture and Horticulture, Earley Gate, Reading RG6 2A7; England) SUMMARY Chickpea (Cicer arietinum Lev. Chaffa) seeds harvested at 77. 105 and 133 days after tlowering were condi-tioned to 14.9-24.1 per cent moisture content and stored at 30 and 40 "C constant temperatures. The rate at which seeds from different harvests deteriorated was similar after storage in comparable temperature and moisture content conditions. The mean viability periods (Ps,,) for seed lots differed markedly between harvests and were related to the initial viability, K" of the seeds from the diJferent harvests. The initial viability of seeds harvested at 77 days was 99.8 per cent (K, equivalent to 2.96), those harvested at 105 days was 97.5 per cent ( K, equivalent to 1.97) and at 133 days it was 33.8 per cent (K, equivalent to -0.42 ). The implieations of delayed harvesting on subsequent storage longevity of the seeds are further discussed. Original scientific paper. 'Received 18 Apr 88; revised 13 Apr 91 Introduction Most seeds start deteriorating soon after matu-rity in the field except those with some mecha-nisms for dormancy. There are various views on when a seed (including embryo and endosperm) has attained physiological maturity. But when-ever maturity is reached, the rate of subsequent deterioration tends to depend on the ambient cn-r vironment of the mother plant (Tekrony et al. 1979; Moore, 1972; Roberts, 1972; Green, Cavannah & ~innel, 1966). It is difficult to meas-ure the level of incipient deterioration taking place in the seed soon after maturation except with very sophisticated instrumentation. With successive sampling for seed-dry matter RESUME OSEl-BONSU, K .. ELLIS, R. K. & ROBERTS, E. K.: E./fel du temps de La nicolte sur la mise en slockage du pois (eieer arietinum L). Du pOls (Ocer arietinum L. cv Chaff a), reeoltes a 77, 105 et 133 jours apres la floraison ont ete mis a des ctats de 14.9 it 24.1% de tcneur en eau et puis mise en stockage it des temperatures constants de 30 et 40 DC. Le taux de la deterioration du po is de differents recoltes etait similaire apres la mise en 'stock age a des conditions de la temperature et teneUf en eau comparables. Les variabilites moyennes des peri odes (P ,,,) du pois, cependant, etaient tres bien different entre les recoltes et etaiellt en rapport avec les viabilites initiales (K,) des' recoltes ditl'erents. La viabilite initiafe du pois fecolte Ii 77 jours etait 99.8% (K. equivalent a 2.96) celie recoJte it 105 jours eiait 97.5% (K, equivalent Ii 1.97) et Ii 133 jours, elle etait 33.8% (K, equivalent a -0.42). Les impli-cations de la recolte tardive sur la longevite de la mise en stockage subsequent du pois ont ete discutees. content, it has been found that th~ lowest·mois-ture content in the seed is a good indicator of when the seed is mature. Thus, a number of work-ers have differentiated between physiological maturity with maximu)TI dry matter production an(j harvest maturity which tends to give drier seeds (Milner & Geddes, 1946; Green et al., 1966; Aus-tin, 1972; Tekrony et ai., 1979). There is also evidence that delayed harvest-ing reduces the initial' viability of the seed (Tekrony, Egli & Balles, 1980 ); this tends to determine the storage potential of the seed (Roberts, 1972; Ellis, 1976; Ellis & Roberts, 1980, 1981; Ellis, Osei-Bonsu & Roberts, 1982). The rate of deterioration, measured by the standard IGhanaJnlagric, Sci. 24-27,31-35 : __ . I Accra: National SCience & Technology Press I 32 K. Osei-Bonsu, et a/. (1991) Ghana Jnl agric. Sci. 24-27, 31-35 deviation of the distribution of seed deaths over time ( a), remains the same under similar storage conditions. ::!"hus, the duration of storage for dif-ferently processed seed lots of a species is pre-determined by their initial quality ( Ellis & Roberts, 1980, 1981; Ellis, Osei-Bonsu & Roberts, 1982). The present study evaluates the initial quality and subsequent storage potential of chickpeas harvested at different intervals. Materials and methods Seeds of chickpea (Cicer arietinum L. cv. Chaffa) obtained from the International Institute for Crop Research for the Semi-Arid Tropics ( ICRISAT), Hyderabad, India, were planted on the University of Reading farm in three blocks measuring 2 m x 6 m each on 23 May 79 at a spacing of30 cm x 10 cm. Triple superphosphate (Pps) and muriate of potash (KP) fertilizers were ploughed into the soil at the rate of 25 kg/ha. Nitrogen from (NH4)2S04 at the rate of 25 kg/ha was applied at planting and 75 kglha applied later at flowering. Seedling emergence and establish-ment were very good and flowering started on 9 Jul 79. The first harvest was taken 77 days after flowering when 65 per cent ofthe pods had yel-lowed and at monthly intervals thereafter. In all cases, plants were harvested from 3.6 m2 plots and the pods were shelled by hand in the labora-tory. Initial as well as subsequent moisture con-tents (fresh weight basis) were determined in ac-cordance with the INSTA (1976) rules. Seeds at each harvest were dried to three ap-proximate moisture contents of 25,20 and 15 per cent over silica gel by intermittently sampling. Ten hermetically-sealed samples of 200 seeds each were stored in incubators kept at 30 and 40°C and were sampled regularly, depending on the storage for germination using the rolled pa-per towel technique in alternating temperature ( 20 0 C for 16 hand 30 0 C for 8 h ) incubators. Constant storage temperatures were used in these experiments because seed deterioration was tem-perature dependent (Roberts. 1972). Results and discussion A normal distribution of seed deaths with time was observed from the storage experiments. It was, therefore, possible to assess the survival curves by a probit analysis (Finney, 1962) and to fix a common intercept to survival curves from each harvest (Roberts, 1972; Ellis, 1976; Ellis et aI., 1982). Seeds with high (20-24 %) moisture contents showed signs of dormancy, and initial germination tests gave values which were much lower than the germination percentage of sam-ples taken after sometime in storage. By omitting the first few germination results which showed dormancy trends from the probit analysis (Roberts, 1961), realistic common intercepts could be fitted to the survival curves. It was then apparent that in comparable stor-age environments, seed survival curves as meas-ured by the standard deviation of the distribu-tion of seed deaths over time (a) were very similar for the different harvests (Fig. 1 ). Thus, the rate of deterioration of seed lots was the same as far as storage environments were similar, con-firming earlier suggestions by Ellis & Roberts ( 1980, /981 ) and Ellis et aL ( 1982). For example, seeds of 11arvest 1 stored at 14.9 per cent m.c. and 40 ° C had a standard deviation ofthe distri-bution of seed death of 4.07 days whilst Harvest 2 at 15.2 per cent m. c. and 40°C had 5.84 days. Similarly, at 21.2 per cent m. c., Harvest I gave a () value of2.12 days while Harvest 3 at 2004 per cent and 40°C gave 1.79 days. Considering the inac-curacies in moisture determination over the pe-riod when these experiments were conducted, these a values were reasonably accurate. Never-theless, the a values were generally lower in seed moisture content for Harvest 3 than Harvest I and Harvest 2. This was probably due to errors in fitting survival curves to few data points in a dis-tribution which was below 30 per cent viability or very close to death ( Ellis & Roberts, 1980 ). When the time taken to 50 per cent (P 50) seed survival at comparable storage environments across harvests was examined, there was consid-erable reduction between seed lots (harvests). Storability of chickpea seeds "., .!!! 98· 0 d li: 95· 0 >- 90·0 :5 :.2i 80· 0 .8 Q d: - 50'0 >. ..... ::: 30' 0 ..c . S 20·0 > Qj 10·0 15-0 ~ 2-0 ... &. 1-0 0'5 20 40 60 Duration 33 II 11l \ \0 d \ \ . . , ~ . ~ ~ 20 40 60 20 of storage ( days) Fig. I. Chickpea seeds cv. Chaffa harvested at three intervals for storag~ experiments at 30"C (~- .. --) and 40 QC (--.-~ .. ): I. Harvest 1 at 77 days after flowering stored at m.e. of 14.9% 0 21.2% 0, .:I; and 23.1 % •. II. Harvest 2 at 105 days after flowering stored with m.e. of 15.2% 0: 20.0% 0, b.; and 24.0% •. III . Harvest 3 at 133 days after flowering stored with m.e. of 20.4% 0, "" and 23.4% • The P values from Harvest I were higher than 50 those from Harvest 2. The disparity was sharp between Harvest 3 (where time to 5 per cent vi-ability (Ps) was used instead) and the other har-vests (Table I). Since the slopes of the curves in comparable storage environments were not sig-nificantly different, it would appear that the dif-ferences were due to the intercept constants, Kp for the three harvests which affected the Pso val-ues from the formula K, P5oi'cr (Ellis & Roberts ,1980 ); where K, is a measure of how far in stand-ard deviation terms the intercept point (zero storage time) is from the mean viability (P 50)' It was observed that there was a sharp decline in the initial viability K" between Harvest 1 and Harvest 2, and between either Harvest 1 or Harvest 2 and Harvest 3. The first harvest (Harvest 1) had an initial viability of 99.8 per cent (or Ki of2.96); Harvest 2 had a value of97.5 per cent (or Kj of 1.97), whilst Harvest 3 was only 33.8 per cent viable (or K, of -0.42). While this finding confirms suggestions that the most important criterion for estimating the storage potential of a seed lot is the initial quality of the seed (Ellis & Roberts, 1980), it also amplifies the need for timely harvest and process-ing as an agronomic requirement for obtaining seeds of good quality for breeding and conser-vation programmes (Tekrony et al. 1980; Green, Cavannah & Pinnel, 1966). Only about 65 per cent of the pods had yel-lowed at the time the first harvest was taken at 77 days after flowering and seeds had a very high moisture content of 48.5 per cent but seed viabil-ity was highest. By the second harvest at 105 days after flowering, all the leaves had dropped. 34 K. Osei-Bonsu etal. (1991) Ghana Jnl agric. Sci. 24-27,31-35 TABLE 1 The Effect of Harvesting Date on the Storage Characteristics of Chickpea Temperature Harvest Days Initial Initial m.c.% Standard 30 IJC 40 "C (lots) after m.c.% viability % storage deviation P51! PJ/ flowering (a) days (days) (. ays) Actual Predicted" Standard Actual Predicted" deviation (a) days . 14.9 - 4.07 12.1 36.1 1 77 48.5 99.8 21.2 9.20 27.2 31.4 2.12 6.3 6.6 25.1 7.92 23.6 20.6 - - -15.2 - . - 5.84 II.S 21.8 2 105 24.6 97.5 2jl.O 11.97 23.5 27.6 2.70 5.3 5.8 24.1 7.92 15.6 11.2 - - -3 133 368 33.8 20A P,(days) P,(days) 6.37 8.8 15.6 1.79 2.5 3.3 23A 4.48 4.5 8.1 - - -.; Predicted from equations V K, -p/lC,;- Cw log .0 m • Cfl t - CQI>; where V is the viability at any given duration Po; K, is the initial viability of the seed lot; m.e. is moisture content (% f.w. basis) and t is temperature "C. KE, Cw ' CH and CQ are constants. KE 9.070; C" 4.829; CH = 0.045; CQ = 0.000324 ( Ellis et al., 1982). the pods had browned, the seeds had a lower moisture content of24.6 percent and had deterio-rated considerably (Ki of 1.97 as against 2.96 for Harvest 1). It seems logical and advantageous, therefore, to harvest the crop between 77 and 105 days after flowering to maximize seed quality. Certainly, other support services like a good drier and sheller to immediately process the seeds are very essential for success. The predictions of longevity (P 50) using the universal constants developed for ehickpeas from a previous experiment (Ellis et al., 1982) were compared with the results obtained in the study. Table I shows that the predictions from the uni-versal equation closely agree with actual values recorded in these experiments, One anomalous result was the 14,9-15.2 per cent m.c. of seeds stmej at 40°C from Harvest I and Harvest 2. Seed survival curves (Fig. 1 ) were normally dis-tributed and fitted the probit analyses accurately. However, the actual Pso recorded seemed to pre-dict those of seeds stored at 18 to 20 per cent m.c. at 40°c' Owing to this curious seed survival pattern, seeds from Harvest 3 at 15 per cent m.c. were dead before first sampling since predictions were based on the universal equations, Simi-larly, predictions for Harvest 3 were widely out of range with the expectations except for the 20.4 J::.., 40 0 C treatment. These observa-tions may be the result of predicting from sur-vival curves towards the tail end of the distribu-tion where seed survival tends to be very erratic. REFERENCES Austin, R. B. (1972) Effects of environment before harvesting on viability. In Viability of seeds (cd. E. H. Roberts), pp. /14-149. London: Chapman and Hall. Ellis, R, H. (1976) The prediction of seed Viability in storage (PhD Thesis). Reading: University of Read-ing. Ellis, R. H., Osei-Bonsu, K. & Roberts, E, H. (1982) The influence of genotype, temperature and mois-ture on seed longevity in chickpea, cowpea and soyabean. Ann. Bot. 50, 69-82. Ellis, R. H. & Roberts, E. H. (1980) Improved equa-tions for the prediction of seed longevity. Ann. Bo(, 45, 13·30. Ellis, R. H. & Roberts, E. H. (198/) The quantifica-tion of ageing and survival in orthodox seeds. Seed. Sci. Technol. 9, 373·409. Storability of chickpea seeds Finney, D. J. (1962) Pr.obit analysis. 2nd ed. Cam-bridge: Cambridge University Press. Green, D. E., Cavannah, L. E. & Pinnell, E. L. (1966) Effect of seed moisture content, field weathering and combine cylinder speed on soyabean seed quality. Crop Sci. 6, 7-10. INSTA (l966) International rules for seed testing, Proc. into Seed Test. Ass. 31, 1-152. Milner, M. & Geddes, W. F. (1946) Grain storage stud-ies. Ill. The relation between moisture content, mold growth, and respiration of soybeans. Cereal Chern. 23, 225-247. Moore, R. P. (1972) Effects of mechanical injuries on 35 viability. In Viability of seeds (ed·. E. H. Roberts). London: Chapman and Hall. Roberts, E. H. (1961) The viability of rice seeds in relation to temperature, moisture content and gase-ous environment. 1. expo Bot. 13, 75-94. Roberts, E. II. (1972) Viability of seeds. London: Chapman and Hajj. Tekrony, D. M., Egli, D. B. & Balles, J. (1980) The effect of the field production environment on soybean seed quality. In Seed production (ed. P. D. Hebblethwaite). London: Butterworths. Tekrony, D. M., Egli, D. B., Balles, J., Pfieffer, T. & F'ellow, R. J. (1979) Physiological maturity in soyabeans. Agron. 1. 71, 771-775. 

Effect of time of harvesting on the storability of chickpea (Cicer arietinum L.) seeds

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Effect of time of harvesting on the storability of chickpea (Cicer arietinum L.) seeds

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