Drought mitigation in Okra (Abelmoschus esculentus L.) through chemical approach

Abstract

Okra or Bhindi (Abelmoschus esculentus L.) is one of the most popular summer vegetable crop grown widely in Kerala for its edible green fruits. Drought is a major yield limiting factor in agriculture and vegetables are more sensitive to drought stress as compared to most of the field crops because of their high water requirement. Hence, the study entitled “Drought mitigation in okra (Abelmoschus esculentus L.) through chemical approach” was carried out with the objective to investigate the influence of different chemicals namely, salicylic acid, ascorbic acid and thiourea on mitigation of drought and to evaluate their effect on morphological, physiological and yield charcteristics of okra. The field experiment was laid out in randomized block design with 8 treatments and 3 replications at RARS, Pilicode during December 2019 to March 2020. The okra variety Arka Anamika was raised as per standard package of practices recommendations of Kerala Agricultural University and also under soil test based nutrient management system. The experiment consisted of 8 treatments viz., normal irrigation (T 1 ) as control, drought stress (T 2 ), T 2 + salicylic acid foliar spray @ 1 mM (T 3 ), T 2 + salicylic acid foliar spray @ 2 mM (T 4 ), T 2 + ascorbic acid foliar spray @ 1 mM (T 4 ), T 2 + ascorbic acid foliar spray @ 2 mM (T 5 ), T 2 + thiourea foliar spray @ 500 ppm (T7), T 2 + thiourea foliar spray @ 1000 ppm (T8). Foliar application of chemicals were given at 10, 20 and 30 DAS and stress was induced by withholding irrigation from 25 days of sowing and re-irrigation was given at 50 per cent field capacity. Morphological, physiological and biochemical parameters were recorded at 25, 50 and 75 DAS and the yield and fruit quality characters were recorded at the time of harvest. A perusal of morphological data showed that T 3 had maximum plant height, number of leaves plant -1 , number of pickings and highest duration of the crop followedby T 6 when compared to all other treatments. The maximum number of branches per plant and the highest root volume were recorded in T 1 which was on par with T 3 followed by T 6 . Foliar spray of chemicals did not significantly influence number of days for 50 per cent flowering and first harvest. Up to 75 DAS, maximum relative growth rate was observed T 3 . All the treatments performed better than drought stress treated crops. At all the growth stages, maximum specific leaf weight was exhibited T 3 . Leaf area was observed maximum for T 3 and was on par with T 4 , T 5 , T 6 at 25 DAS and T 1 , T 4 and T 6 at 50 DAS and T 6 at 75 DAS. The relative leaf water content was recorded the highest for T 3 at 25 DAS and for T 1 at 50 and 75 DAS. At 50 DAS, T 1 was on par with T 3 , T 6 and T 7 and at 75 DAS T 1 was followed by T 3 and T 6 . T 3 had maximum total dry matter production which was on par with T 1 and T 4 .at 25 and 50 DAS, respectively. Root shoot ratio was recorded maximum in T 3 which was on par with T 1 at 25 and 50 DAS. SPAD chlorophyll meter reading (SCMR) was recorded maximum in T 3 at 25 and 50 DAS and in T 1 at 75 DAS. T 1 was on par with T 3 , T 4 and T 6 at 75 DAS. Considering the yield and fruit quality attributes, T 4 recorded maximum value for fruit length and was on par with T 1 , T 7 and T 8 . The highest average fruit girth and fruit weight were exhibited in T 3 and lowest was in drought stressed crop (T 2 ). The treatment T 1 , T 3 , T 4 and T 6 recorded maximum number of fruits plant -1 which were on par with T 5 and T 7 . The highest total fruit yield was recorded in foliar spray of salicylic acid (1 mM) followed by ascorbic acid (2 mM). These treatments recorded 45 per cent and 41 per cent higher yield over drought stressed treatment, respectively. The crude fibre content was recorded highest for drought stressed crops (T 1 ) and the lowest was recorded in T 3 . The ascorbic acid content was observed maximum in T 1 followed by T 5 and T 6 . The highest net returns and BCR was obtained in T 3 followed by T 6 . The frequency of irrigation given was highest in T 1 followed by T 2 and T 8 . The lowest frequency of irrigation given were in T 3 , T 6 and T 7 . The irrigation interval was more with T 3 , T 6 and T 7 (5 days).It can be concluded that morphological, physiological, biochemical and yield traits of okra were severely affected under drought stress. Among the three drought mitigating chemicals, salicylic acid (1 mM) recorded maximum values for morphological traits viz., plant height, number of leaves plant -1 , root volume and duration of crop, followed by ascorbic acid (2 mM), which also significantly improved morphological traits of okra compared to all other treatments. Physiological traits such as total dry matter production, leaf area plant -1 , relative growth rate, specific leaf weight, root shoot ratio and SPAD chlorophyll meter reading increased over drought stress crop when sprayed with salicylic acid (1 mM) and ascorbic acid (2 mM). Salicylic acid (1 mM) and ascorbic acid (2 mM) is beneficial for getting higher fruit yield and maximum economic returns over drought stressed and normal irrigated crops. Therefore, application of salicylic acid (1 mM) and ascorbic acid (2 mM) significantly mitigated the harmful effect of drought stress in okra.