Effects of water stress on photosynthesis, flowering and fruit-set of field-grown carambola (Averrhoa carambola L.)


M. Masri


 The effects of drought on photosynthesis, flowering and fruit-set of two commercially grown carambola clones were studied under field conditions at the Fruit Research Centre, MARDI Bukit Tangga, Kedah. The plants were subjected to two moisture levels, namely ‘irrigated’ (daily irrigation at field capacity) and ‘drought’ (no irrigation for a 21-day period), during the drought season of January 1992. Changes in the soil moisture, photosynthetic rate as well as the effects on flowering and fruit-set were monitored during the experimental period. Results showed that photosynthesis, flower density, fruit density and fruit-set were significantly reduced by water stress. Maximum photosynthetic rates were observed at PAR 700 μmol/m2 per second in both clones with higher rate of 11.1μmol/m2 per second for B17 as compared with 8.1 μmol/m2 per second for B10. However, under water stress conditions, these rates were decreased to 6.7 (B17) and 6.4 μmol/m2 per second (B10). Water stress also reduced flower density from 29.8 to 19.5 (B10) and from 38.8 to 17.3 (B17) flowers/cm2 BCSA while fruit density from 24 to 18 (B10) and from 17 to 10 (B17) fruit/cm2 BCSA. Lower fruit density was accounted for by the low fruit-set observed in the nonirrigated plants where fruit-set was reduced tremendously from 83% to 38% (B10) and from 90% to 25% (B17) by water stress. It was also shown that the magnitude of reduction by water stress in all parameters measured was more severe in B17 suggesting that this clone is more sensitive to water stress than B10.

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