Effect of Shading on the Development and Yield of Two Okra (Hibiscus esculentus L.) Cultivars Grown under High Temperatures

The effect of shading on the growth and yield of okra (Hibiscus esculentus L.) under hot, summer conditions in the Mediterranean region was studied. Seeds of cv. 'Boyiatiou' and 'Clemson Spineless' were scarified in H2SO4 and sown in peat on 4 May. At the 3-4 leaf stage (35 days after sowing) the plants were transplanted to 16L pots containing a substrate of peat and perlite (1:1 v/v). The pots (3 replicates of 4 plants each) were spaced in the field at 1.0 x 0.6 m and irrigated with a nutrient solution (20N-20P-20K). The treatments consisted of shading at 0% (uncovered control), 30% and 70% (covered with plastic netting). Plant growth (height, leaf number, node number and internode length) was recorded and pods were harvested every 2-3 days at the stage of market acceptability. The plant height of both cultivars increased significantly with 70% shading. In 'Boyiatiou' this was due to internode extension, whereas in 'Clemson Spineless' node number increased (30% and 70% shading) and internode length (70% shading). The number of flowers per plant was unaffected by shading in either cultivar but the total number of pods per plant decreased in 'Boyiatiou' under 70% shading leading to a reduction in total pod weight. In 'Clemson Spineless' the weight of pods per plant was lower under both 30% and 70% shading relative to the control but the decrease in pod number was not significant (p=0.05). In both cultivars a reduction in the number of leaves of the 70% shaded plants at the end of the experiment was due to increased abscission of the old, lower leaves. Overall, it appears that shading of okra plants during cultivation under hot Mediterranean conditions is not beneficial for okra production.