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Reduced stomatal density in wheat and its potential for improving control of foliar pathogens

Jane Thomas: National Institute of Agricultural Botany

<div>Higher plants evolved in atmospheric conditions where carbon dioxide levels were significantly lower than recent levels. As a result, high stomatal densities were needed for efficient photosynthesis. At higher levels of carbon dioxide, reduced densities may allow efficient photosynthesis without loss of yield. Stomata also act as entry points for some major foliar pathogens, and decreasing stomatal density may thus reduce infection points and the rate of epidemic development. To test this, we investigated the development of two contrasting pathogens in inoculated tests on transformed lines of wheat cv. Fielder with reduced stomatal densities. There was no effect on the development of powdery mildew (<em>Blumeria graminis</em> f.sp. <em>tritici</em>), which enters through epidermal cell junctions (mean 49% leaf area infected on low density lines and 51% on the null line). However, in the case of leaf rust (<em>Puccinia triticina</em>), which enters through stomata, mean pustule numbers were significantly lower (p<0.05) at 7.1 pustules per cm<sup> </sup>length of leaf on the line with fewest stomata compared to the null line at 12.8 pustules. Reductions were observed in repeat experiments and additional transformants with higher stomatal frequencies showed higher pustule numbers, though these were still less than the null line. Breeding for reduced stomatal frequency in wheat may offer a means of improving control of some pathogens such as rusts in the field.</div>