Y. S. Chauhan

Osmotic adjustment, water relations and carbohydrate remobilization in pigeonpea under water deficits.

Summary Osmotic adjustment (OA) is considered an important mechanism for drought adaptation. The objective of this study was to evaluate the contribution of OA to growth and productivity of extra-short-duration pigeonpea ( Cajanus cajan (L.) Millsp.) during soil moisture deficits. Using two automated rain-out shelters, six pigeonpea genotypes were grown under well-watered conditions throughout the growth period or under water deficits imposed from flowering until physiological maturity. Soil moisture content was monitored using neutron probes. Osmotic adjustment in leaves increased with the depletion of soil moisture and reached close to 0.5 MPa at physiological maturity. Genotypic variation in OA (ranging from 0.1 to 0.5 MPa) was significant. Total non-structural carbohydrates mobilized from stem for reproductive growth varied substantially among genotypes. Contribution of stem-reserves to the grain yield, however, was less than 5%. Below 30 cm depth, 60 to 80% of the plant extractable soil water was not utilized at physiological maturity in the drought treatment. Genotypic variation in leaf relative water content was correlated with OA (r 2 = 0.66 * , n = 6). Leaf OA was correlated with the amount of stem sucrose mobilized (r 2 = 0.67 * ; n = 6). The relationship between OA and leaf area duration was significant (r 2 = 0.94 ** ; n = 5). Genotypic variation in leaf relative water content was correlated with crop growth rate (r 2 = 0.74 * ; n = 6) and radiation-use efficiency (r 2 = 0.84 ** ; n = 6) under moisture deficits. The results indicate that OA could influence radiation use efficiency and crop growth rate of extra-short duration pigeonpea indirectly by increasing leaf relative water content during soil moisture deficits.

Patterns of osmotic adjustment in pigeonpea — its importance as a mechanism of drought resistance

Osmotic adjustment (OA) is considered as an important physiological mechanism of drought adaptation in many crop plants. The present investigation was aimed at assessing the importance of OA in improving productivity under drought. Using two automated rain-out shelters, 26 extra-short-duration pigeonpea [Cajanus cajan (L.) Millsp.] genotypes were grown with irrigation during the growth period or with water deficit imposed from flowering until maturity. Mean leaf Ψs100 (60–92 DAS) under drought correlated significantly (r2=0.72**; n=26) to the mean OA (60–92 DAS) and contributed 72% of the genotypic variation in OA. Significant genotypic variation was observed in the initiation of OA, the duration of OA and the degree of OA. Based on the measured OA at 72, 82, and 92 days after sowing (DAS), genotypes were grouped into five different clusters. Genotypic differences in total dry matter production under drought were positively associated with OA at 72 DAS (r2=0.36**, n=26). Significant positive relationship between OA at 72 DAS and grain yield under drought was found (r2=0.16*; n=26). However, OA towards the end of pod filling phase, i.e. at 92 DAS, had a significant negative relationship with grain yield under drought (r2=0.21*; n=26). Genotypic differences in grain yield under drought was best explained using stepwise multiple regression to account for differences in OA at 72, 82, and 92 DAS (r2=0.41**; n=78). The degree of OA at 72 and 82 DAS contributed positively to the grain yield, whereas OA at 92 DAS contributed negatively to this relationship

Effect of timing of drought stress on growth and grain yield of extra-short-duration pigeonpea lines

Four extra-short-duration (ESD) pigeon pea (Cajanus cajan) lines in 1991 and eight ESD lines in 1992 were grown with adequate soil moisture throughout their growth or subjected to drought coinciding with the vegetative, flowering and pod-filling stages under rainout shelters (India). In both years, drought stress treatments significantly reduced dry matter accumulation and seed yield. The extent of reduction in seed yield varied with the line and stage of stress imposition. Drought stress at the flowering stage caused greater reduction in total dry matter and seed yield than the stress imposed during the preflowering and pod-filling stages. Drought stress coinciding with the flowering stage reduced seed yield by 40-55% in 1991 and 15-40% in 1992 in different lines. ESD genotypes could extract moisture from up to a metre depth during preflowering and flowering stage stress but less during the pod-filling stage stress. Genotype ICPL 88039, followed by ICPL 89021, consistently showed the lowest sensitivity to drought stress at flowering. Protracted drought stress commencing from the preflowering to flowering or from the flowering to pod-filling stages was more harmful than stress at the individual stages. The reduction in yield under drought stress could be attributed mainly to less total dry matter accumulation, but also increased abscission of plant parts. The results suggest variation in sensitivity of ESD lines in relation to timing of stress, which should facilitate targeted screening for different intermittent moisture stress environments

Thermostabilities of cell-membrane and photosynthesis in cabbage cultivars differing in heat tolerance

Summary Responses of two Japanese cabbage (Brassica oleracea L. var. capitata) cultivars, heat tolerant Sousyu and heat-susceptible YR Kinshun, were compared in terms of cell-membrane thermostability, chlorophyll fluorescence, chlorophyll A and chlorophyll B contents, and photosynthetic rates. High (~50 °C) temperature caused greater relative injury and reduction in the values of fluorescence in YR Kinshun than in Sousyu, especially when non-hardened for 24 h prior to the measurement. Hardening at 30–35 °C improved the thermostabilities of cell-membrane and chlorophyll fluorescence and decreased the chlorophyll content, and consequently photosynthetic rates in YR Kinshun. Chlorophyll content and chlorophyll fluorescence of Sousyu were relatively less adversely affected by the hardening and stress temperatures. Sousyu maintained higher chlorophyll content and rates of photosynthesis than the YR Kinshun in hardened condition whereas differences between the two genotypes were small in non-hardened condition. Heating leaves at 50 °C reduced photosynthetic rates of both the cultivars. Sousyu, however, maintained higher rates than YR Kinshun even after the heat treatment. The results suggest that higher thermostability of cell membranes, chlorophyll fluorescence and photosynthetic rates of Sousyu, especially under non-hardened condition, may give it an overall advantage in high temperature environments over YR Kinshun.

Comparison of extra-short-duration pigeonpea with short-season legumes under rainfed conditions on alfisols

Extra-short-duration pigeonpea (Cajanus cajan) genotypes generally yielded more than short-season legumes when sown at the normal time on rainfed medium-deep Alfisols. However, their growth and yield were more reduced by delayed sowings and varied more widely between seasons than those of the short-season legumes, especially cowpea and black gram. All the crops gave lower yields on shallow Alfisols than on medium-deep Alfisols and none was consistently superior. Partitioning of dry matter into grain yield was less affected by time of sowing, soil and season in extra-short-duration pigeonpea genotypes than in short-season legumes. Less sensitivity of biomass accumulation to various abiotic constraints is therefore a major objective in improving the adaptation of extra-short-duration pigeonpea genotypes.

EXTRA-SHORT-DURATION PIGEONPEA FOR DIVERSIFYING WHEAT-BASED CROPPING SYSTEMS IN THE SUB-TROPICS

The performance of newly developed extra-short-duration pigeonpea (Cajanus cajan) genotypes and traditional short-duration pigeonpea cultivars was compared in rotation with wheat in on-farm trials conducted in 1996–97 and 1997–98 in Sonepat (28° N) district in Haryana, and in 1996–97 at Ludhiana (30° N) district in Punjab, India. At both locations, a wheat crop (Triticum aestivum cv. HD 2329) followed pigeonpea. At Sonepat, an indeterminate extra-short-duration genotype ICPL 88039 matured up to three weeks earlier, yet gave 12% higher yield (1.57 t ha−1) and showed less susceptibility to borer damage than did the short-duration cv. Manak. At Ludhiana, extra-short-duration pigeonpea genotypes, ICPL 88039, ICPL 85010 and AL 201 gave similar grain yields to the short-duration T 21 in spite of maturing three to four weeks earlier. Yields of wheat crops following extra-short-duration genotypes were up to 0.75 t ha−1 greater at Sonepat and up to 1.0 t ha−1 greater at Ludhiana. The results of the study provide empirical evidence that extra-short-duration pigeonpea genotypes could contribute to higher productivity of pigeonpea–wheat rotation systems. Most of the farmers who grew on-farm trials in Sonepat preferred extra-short-duration to short-duration pigeonpea types for their early maturity, bold seed size, and the greater yield of the following wheat crop.