Impact of Heat Wave on the Plant Architecture of Field Grown Jatropha curcas Accession

Abstract

Heatwave is one of the common phenomena in the arid and semi-arid regions which greatly hinders crop productivity. Jatropha curcas, which is well known for its medicinal and seed biodiesel uses, is one of the crops that are negatively affected by high temperatures. Therefore, this study was aimed at monitoring the effect of a heat wave on the plant architecture of Jatropha curcas plants grown in the south east of Botswana, a semi-arid region. The field experiment was conducted in 2016 (2016/2017) and 2017 (2017/2018) cropping season using plants that were established in 2011. Data on changes in leaf numbers, changes in leaf areas, photosynthetic rates, leaf temperatures, and soluble sugar levels were measured over the spring, summer, and autumn seasons of 2016 and 2017. In 2016, the general trend of the above measured parameters was that they peaked in summer and declined in autumn. However, in the summer of 2017, the accessions were hit by a heat wave, which depressed the photosynthetic rates, concomitantly decreasing leaf numbers, leaf areas, and leaf area indices. This reduction continued into the autumn of 2017. The plant architecture of the J. curcas accessions differed in the two years, indicating that the accessions responded differently under heat waves. The observations made as the plants recovered was that immediately below the apex, 2–3 leafed lateral shoots developed, which would normally be evident much lower down the stem. This suggests that the effect of the heat wave thus appeared to have impacted the plant architecture in the autumn. Soluble sugar levels were also higher in the autumn leaves of 2017 than in the autumn leaves of 2016.