Legumes. Chickpea

stress was not allowed to occur with an optimum irrigation regime the shoot biomass productivity was near 5 t ha-1 with a seed yield of 2t ha-1. However, under the normal receding soil moisture condition, the shoot biomass productivity ranged across years from 1.8 to 3.8 and the seed yield from 0.7 to 1.6 t ha-1 (Krishnamurthy et al. 2010).

Chickpea breeding program at ICRISAT has placed high emphasis on development of early and extra early maturing varieties so that these can escape terminal drought. The early maturing crop, however, cannot accumulate enough total plant biomass due to reduced total photosynthetic period compared to the relatively longer duration varieties.

Terminal drought reduces both shoot biomass and yield in chickpea. For example the average shoot biomass reduction of 40 cultivated chickpea genotypes due to terminal drought was 44 to 61 % across two years whereas the grain yield reductions were 35 to 66% (Krishnamurthy et al. 1999). Similarly the average shoot biomass reduction of 216 (mini core) chickpea germplasm accessions due to terminal drought was 31 to 63 % across 3 years whereas the grain yield reductions were only 26 to 61% (Krishnamurthy et al. 2010). The relatively less reduction in grain yield under drought was due to an increased partitioning under the progressively built terminal drought stress.

Groundnut

Groundnut (Arachis hypogaea L.) is an important rainy-season crop in most of the production systems in the semi-arid tropical regions of south Asia and sub-Saharan Africa, where it is grown under varying agroecologies, either as a sole crop or intercropped with sorghum and pigeonpea. Groundnut yields are generally low and unstable under rain-fed conditions, due to unreliable rainfall patterns. Severity of drought stress depends on the stages of crop development and the duration of stress period (Wright and Nageswara Rao, 1994). Improvement of transpiration efficiency (TE) is seen as a promising strategy to improve shoot biomass and pod yield productivity under episodes of intermittent drought. Efforts were made to identify simple and easily measurable traits that are closely associated with TE such as SCMR (Nageswara Rao et al., 2001; Sheshshayee et al., 2006), SLA (Nageswara Rao and Wright, 1994; Wright et al., 1994) and carbon isotope discrimination (Hubick et al., 1986; Farquhar et al., 1988; Wright et al., 1994). Recent works have demonstrated that root dry weight and SLA were important traits related to WUE under long term drought and considered useful as selection criteria for high WUE under long term drought (Songsri et al.,

2009) .

Groundnut pod yield productivity is more adversely affected by various seasonal droughts than the shoot biomass production. For example, in a field trial where the drought intensity and the timing is managed by withholding irrigation and providing a part by line source irrigation it was established that the drought occurring between emergence to peg initiation was rather beneficial, producing greater yields than the control. However the drought occurrence between the phases of start of flowering to start of seed growth had lead to a reduction of 13 to 49% in shoot biomass and 18 to 78% in pod yield. The drought stress from the start of seed growth to maturity (terminal drought) had caused a reduction of 16 to 73% for the shoot biomass and 24 to 95 % for the seed yield (Nageswara Rao et al. 1985).

Pigeonpea

Pigeonpea (Cajanus cajan (L.) Millspaugh) is a deep-rooted and drought-tolerant leguminous food crop grown in several countries, particularly in India and India accounts for about 80% of the total world pigeonpea production. It is grown mainly by resource poor farmers in

India south east Africa and, to a varying extent, throughout the tropics, usually under rain — fed conditions.

Pigeonpea can be exposed to intermittent drought stress during dry periods of the rainy season and to terminal-drought stress in the post-rainy season. Over the last two decades, shorter-duration pigeonpea (SDP) genotypes have been developed, with some genotypes capable of reaching maturity within 90 days (Nam et al., 1993). However, the developed short-duration genotypes are usually sensitive to intermittent drought. Considerable variation in tolerance to intermittent drought has been observed in short-duration pigeonpea lines and variation in sensitivity in relation to timing of drought stress has been established (Lopez et al. 1996). As in other crops, responses to intermittent drought stress have been shown to depend on the growth stage at which the stress occurs (Nageswara Rao et al. 1985). For example Nam et al. 1993 has shown that the drought incidences at flowering cause a large reduction in productivity than drought at preflowering stage or at pod fill stage. The shoot biomass reduction was 26 to 33% across years whereas the yield reduction was 30 to 48% (Nam et al. 1993).

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