C. Johansen

Effects of the Sodium/Calcium Ratio in Modifying Salinity Response of Pigeonpea (Cajanus cajan)

Summary There was a positive growth response by salt-tolerant (ICPL 227) and salt-sensitive (HY 3 C) pigeonpea genotypes to a decreasing Na/Ca ratio under constant salinity. The relative growth differences between tolerant and sensitive genotypes persisted at different Na/Ca ratios at 6 and 8 dS m -1 salinity levels. A decrease in the Na/Ca ratio under salinity enhanced K uptake and reduced Na uptake, thus increasing the K/Na ratio. The K/Na ratio in shoots of the tolerant genotype was greater than in the sensitive genotype at different Na/Ca ratios at both salinity levels. The tissue Cl levels increased with decreasing Na/Ca at both salinity levels. This increase was greater in the sensitive than in the tolerant genotype. Thus relative growth differences and differences in Na, K and Cl uptake between tolerant and sensitive genotypes persisted across the range of Na/Ca ratios. This suggests that results of screening for genotypic differences at one particular Na/Ca ratio would be applicable to other Na/Ca ratios.

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

Field evaluation of nitrogen fixation and use of nitrogen fertilizer by sorghum/pigeonpea intercropping on an Alfisol in the Indian semi-arid tropics

A field experiment was conducted to obtain the N balance sheet for sole crops and intercrops of sorghum [Sorghum bicolor (L.) Moench] and pigeonpeas [Cajanus cajan (L.) Millsp.]. Intercropping gave a significant advantage over sole cropping in terms of dry matter production and grain yield, as calculated on the basis of the land equivalent ratio and area-time equivalent ratio. The N fertilizer use efficiency and atmospheric N2 fixation by pigeonpea were estimated using 15N-labeling and natural abundance methods. The N fertilizer use efficiency of sorghum was unaltered by the cropping system, while that of the pigeonpea was greatly reduced by intercropping. Although intercropping increased the fractional contribution of fixed N to the pigeonpeas, no significant difference was observed between the cropping systems in total symbiotically fixed N. There was no evidence of a significant transfer of N from the pigeonpea to the sorghum. This study showed that use of soil N and fertilizer N by pigeonpeas was almost the same as that by sorghum in sole cropping, indicating the potential competence of pigeonpeas to exploit soil N. However, when N was exhausted by a companion crop in intercropping, the pigeonpea crop increased its dependency on atmospheric N2 fixation. We conclude that knowledge of how N from different sources is shared by companion crops is a prerequisite to establishing strategies to increase N use, and consequently land productivity, in intercropping systems.

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

Genotypic variation in moisture response of chickpea grown under line-source sprinklers in a semi-arid tropical environment

The line-source sprinkler technique was used to compare moisture responses of a range of advanced chickpea (Cicer arietinum) breeding lines grown on soil with decreasing soil moisture. Experiments were conducted on a Vertisol soil in peninsular India during the 1985-86 and 1986-87 post-rainy seasons. Lines tested displayed a linear response of both aerial biomass and grain yield to moisture applied. Thus, use of only two moisture levels, with and without irrigation, would be sufficient to compare moisture responses of chickpea in this environment. Genotypic responses were evaluated on the basis of slopes and intercepts of line-source data. Lines previously identified as drought resistant showed greatest resistance in the present study. Most test lines from breeders had relatively low drought resistance, as indicated by low intercept and intermediate to high slope values. This is consistent with the test lines having been selected under different levels of supplementary irrigation in different generations. It is suggested that development of substantially improved drought resistance in this environment will require rigorous selection pressure under a given drought environment. A breeding programme under naturally decreasing soil moisture conditions in this environment is feasible because the pattern of decreasing soil moisture is, or can be made, similar across seasons, thus minimizing environmental variability in relation to genotypic variability.

Physiological basis of differences in salinity tolerance of pigeonpea and its related wild species.

Summary The physiological responses of a tolerant (ICPL 227) and a sensitive (HY 3C) cultivated pigeonpea [ Cajanus cajan (L.) Millsp.] genotype and of tolerant ( Atylosia albicans, A. platycarpa and A. sericea ) and sensitive ( Rynchosia albiflora, Dunbaria ferruginea, A. goensis and A. acutifolia ) wild relatives were examined over a range of salinity levels. Transpiration rate decreased with increasing salinity in tolerant and sensitive pigeonpea genotypes and there were no consistent differences between them in this respect. Although leaf proline concentrations increased under salinity in the cultivated pigeonpea and in some of the wild relatives, there was no relation between salinity tolerance and proline accumulation. The greater salinity tolerance of A. albicans, A. platycarpa and A. sericea was associated with efficient sodium and chloride regulation in the plant system. Shoot sodium concentrations of the tolerant wild species were five to ten times less than those of the sensitive species, while root sodium concentrations in the tolerant species were two to three times higher than in the sensitive species. The potassium concentrations in the tolerant species increased with salinity, while in the sensitive species they decreased. Leaf magnesium concentrations remained unaffected with increasing salinity in the tolerant species, while in most of the sensitive species they decreased. Thus efficiency of regulation of ion transport to shoots seems to explain the differences in salinity response among pigeonpea genotypes and related wild species.

Diagnosis and alleviation of boron deficiency causing flower and pod abortion in chickpea (Cicer arietinum L.) in Nepal

Symptoms of flower abortion and failure of pod set in chickpea in Chitwan, Nawalparasi and Makwanpur districts of Nepal suggested a nutrient disorder as a prime cause of the problem. Thus, a diagnostic nutrient trial with a susceptible chickpea variety, Kalika, was conducted in the 1994/95 season. Boron deficiency was established as the dominant nutritional problem causing flower and pod abortion. No pods or grains were formed in the absence of applied B. However, there was also a significant grain yield response to Mo. In the following season, a factorial combination of different rates of B and Mo was tested. Responses were less marked in this trial than previously, with no significant response to Mo application. Application of 0.5 kg B ha-1 was found to optimally correct the syndrome. It is suggested that B-deficiency may be a major factor limiting yields of grain legumes in Nepal; this is currently being assessed.

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.