Effect of chemical desiccation at the post-anthesis stage on some physiological and biochemical changes in the flag leaf of contrasting wheat genotypes

Abstract

In northern India, wheat is often grown under terminal drought conditions. Researchers have shown that there is genetic variation in the re-distribution of pre-anthesis assimilates to grow under these drought conditions. The technique of applying a desiccant, and then measuring effects on grain yield has been used for evaluation of plant response. This study examined in effect of the desiccant on photosynthesis and metabolites in the flag leaf. To induce artificial senescence during grain-filling stage, two contrasting cultivars of wheat cv., Lok-1 (drought susceptible) and WH-533 (drought tolerant), were raised in pots under irrigated conditions. They were sprayed with 0.1% potassium iodide, a chemical desiccant, at the one-third filled seed cavity stage. Three experimental treatments were water spray on the whole canopy (control), KI spray on the whole shoot (WPS), and KI spray on the shoot except for the ear head (escaping ear head, EHE). Changes at 6 h, 1, 2, 4 and 6 days after spray (DASP) were examined in the flag leaves. There was a consistent decrease in rate of photosynthesis and chlorophyll content, and increase in sucrose and proline with increased DASP. In WH-533 at 6 DASP, photosynthesis was reduced by 84 and 48% and chlorophyll content by 52 and 31%, while sucrose content was 5.2 and 5.4 and proline 14 and 13.6 times more than in control in EHE and WPS treatments, respectively. The corresponding changes in Lok-1 were reduction of 98 and 84% in photosynthetic rate, 64 and 51% in chlorophyll content, and sucrose 4.5 and 6.2 and proline 15 and 11 times higher than in control plants. These responses are similar to that reported for water stress. The more pronounced reduction in photosynthesis and chlorophyll content in KI treated plants of Lok-1 than WH-533 is also consistent with the known differential drought tolerance of these cultivars. Therefore, KI induced artificial desiccation technique can be used for screening genotypes for terminal drought tolerance.