Influence of water stress on photosynthesis, transpiration, water-use efficiency and yield of Brassica juncea L.

Abstract

Abstract Indian mustard ( Brassica juncea L. cv. Parkash) grown in large containers was subjected to six watering treatments: (i) no watering after crop establishment; (ii) dry up to floral bud appearance and irrigated thereafter; (iii) dry up to full bloom and irrigated thereafter; (iv) early irrigation, dry during flowering period and irrigated during pod formation; (v) irrigated up to flowering and dry afterwards; (vi) irrigated control. Several plant processes were measured diurnally and seasonally on many clear days. Diurnally, canopy photosynthetic rate (P N ) followed photon flux density (PAR), and transpiration (T) followed air temperature ( T a ). At higher PAR, P N in dry treatments was greater during the first than the second half of the day. Photosynthesis attained compensation point at −4.0 MPa leaf water potential ( Ψ 1 ). Similarly, T during the first half of the day was greater than in the second half of the day at similar T a . Water-use efficiency (WUE) was quite low at high PAR during the second half of the day. Photosynthesis and WUE peaks were observed during the full bloom period while T gradually increased towards maturity. Seed yield was primarily reduced by water stress because of decrease in number of pods per plant and number of seeds per pod. The number of pods per plant and number of seeds per pod were linearly related to seed yield, and cumulative Ψ 1 and P N related to both seed yield and total biomass.