Effects of temperature and photoperiod on vegetative and reproductive growth of groundnut (Arachis hypogaea L.)

Effects of temperature x photoperiod interaction on vegetative and reproductive growth were examined in three selected groundnut genotypes by growing them in controlled-environment growth chambers with three temperature regimes (22/18, 26/22, and 30/26 degrees C, day/night) under long (12 h, long day), and short (9 h, short day) photoperiods. The effect of photoperiod on the total dry-matter production (TDM) was significant with the genotypes producing 32-72 % greater dry matter under LD than SD. Temperature x genotype interaction effects were significant, with the dry-matter production being greatest at 26/22 degrees C and least at 30/26 degrees C and 22/18 degrees C in two of the three genotypes. Leaf area (LA) was greater under LD than SD at all temperature regimes. LA accounted for 76 % of the variation in shoot + root dry weight (R-2 = 0.76, P < 0.01). A lack of relationship between LA and pod weight or pod numbers suggested that the pod development is controlled by factors other than carbon assimilation. The temperature x photoperiod interaction was significant for root growth, with the root weight being maximal and photoperiod effects being minimal at 22/18 degrees C, while at 26/22 degrees C, root weight declined and photoperiod effects became prominent. Low temperature (22/18 degrees C) affected the reproductive development by reducing the proportion of reproductive nodes in total (vegetative + reproductive) nodes. The conversion of pegs into pods, as indicated by pod to peg ratio (PPR), was lower in LD than in SD conditions. Results suggested that the PPR could be used as an indicator of genotypic sensitivity to photoperiod in groundnut.