EVALUATION OF RESISTANCE OF KENYAN SUNFLOWER TO LEAF TISSUE DEGRADATION BY OXALIC ACID AND THE OIL YIELD

Abstract

Oxalate oxidase is a pathogenesis‐related enzyme that occurs naturally in plants and whose activity is observed to increase when hosts are attacked by oxalic acidproducing pathogens, countering the effects of the acid and thus conferring resistance to infection. This study, through two assays, sought to investigate the level of oxalate oxidase activity in six Kenyan sunflower (Helianthus annuus L.) varieties namely: Kenya Fedha, Rekord, Issanka, H8998, H4038 and H4088. The reaction of oxalate oxidase with its substrate, oxalic acid, yields hydrogen peroxide which can be assayed calorimetrically as a measure of enzyme activity. In this study, an assay which focused on release of hydrogen peroxide from sunflower leaf discs incubated in a buffer containing oxalic acid was conducted. A detached leaflet assay was also conducted to assess the ability of oxalate oxidase to prevent necrosis in response to exogenous application of oxalic acid to plant tissue whereby lesion sizes were measured. The oil content of the six sunflower varieties was also determined to identify the ones with the highest oil‐yielding potential. The test sunflower varieties differed significantly (p<0.05) in oxalic acid degradation and in their hydrogen peroxide production, indicating varying degrees of oxalate oxidase activity. H4088 and H8998 had the highest seed oil content and were identified as superior sunflower varieties that could be recommended for edible oil production in Kenya. However, H8998 may require genetic transformation to enhance its disease resistance capacity.