Effect of Water Stress and Infection by Ustilago striiformis or Urocystis agropyri on Leaf Turgor and Water Potentials of Kentucky Bluegrass¹

Abstract

Plant tolerance to water stress can be measured, in part, by calculating the plants ability to maintain turgor during periods of water stress. Kentucky bluegrass (Poa pratensis) systemically infected by either Ustilago striiformis (Stripe smut) or Urocystis agropyri (Flag smut) exhibits greater mortality than noninfected plants during periods of water stress suggesting decreased drought tolerance with infection. The effects of water stress and systemic infection by the smut producing pathogens, Ustilago striiformis or Urocystis agropyri, were evaluated for their effects on leaf turgor and water potentials of Kentucky bluegrass ‘Merion’ grown in nutrient solution. Infection by either pathogen decreased leaf turgor and water potentials during light and dark periods as compared with noninfected controls. In addition, noninfected plants maintained higher leaf turgor and water potentials than infected plants as nutrient solution osmotic potentials were lowered with polyethylene glycol. Moisture release curves for single leaves from noninfected, U. striiformis‐, and U. agropyri‐infected plants were established to evaluate plants for osmotic adjustment by estimating leaf osmotic potentials and relative water contents at zero turgor as plants were grown in nutrient solution and nutrient solution amended with polyethylene glycol to increase water stress. Turgid weight/dry weight ratios also were calculated for noninfected and diseased leaves before and after water stress. Water stress lowered leaf osmotic potentials and relative water contents at zero turgor and decreased the turgid weight/dry weight ratios of noninfected and infected leaves. Noninfected plants exhibited lower osmotic potentials at zero turgor and maintained smaller turgid weight/dry weight ratios after water stress than infected plants, suggesting that infection by either pathogen inhibited osmotic adjustment and cell wall thickening in leaves of Kentucky bluegrass in response to water stress.

Pressure‐volume curves and drought resistance in two wheat genotypes

“…However, this technique gives information about water relations and may be applied t o field-grown plants, and it has been commonly used (Auge et al 1986. Frank et al 1984. Nus and Hodges 1985.…”

Low water availability increases susceptibility to peanut smut (Thecaphora frezzii) in peanut crop

“…Under the combined biotic and abiotic stress, proline, chlorophylls and sugars were increased (marginal for sugars, p = 0.07), which prompts the hypothesis that these biochemical/physiological changes may be related to the increase in damage associated with drought. In contrast, in the Ustilago-P. pratensis system, the pathogen inhibited the plant osmotic adjustment (Nus & Hodges, 1985), although the authors did not directly assess proline. In our pathosystem, we hypothesize that the changes in proline, sugars and chlorophylls may help the pathogen to cope with the low water potential or serve as a carbon or nitrogen source (Christgen & Becker, 2019).…”

“…This response agrees with other smut fungal infections in grasses such as those caused by Ustilaginales fungi. The four reported pathosystems (U. striiformis-P. pratensis, U. agropyri-P. pratensis, U. maydis-Zea mays and Sporisorium scitamineum-Saccharum officinarum) showed higher disease damage when the infection occurs during water scarcity (Bertani et al, 2021;Kostandi & Soliman, 1998;Nus & Hodges, 1985).…”

“…pratensis , U. agropyri–P . pratensis , U. maydis–Zea mays and Sporisorium scitamineum–Saccharum officinarum ) showed higher disease damage when the infection occurs during water scarcity (Bertani et al., 2021; Kostandi & Soliman, 1998; Nus & Hodges, 1985).…”

“…Drought can lead to either increased susceptibility or tolerance of plants to disease, depending on the pathogen under study. Among the smut fungi (biotrophic basidiomycetes that usually infect reproductive tissues), two studies have shown an incremental increase in plant susceptibility to a pathogen when infection overlaps with water deficit: in Kentucky bluegrass ( Poa pratensis ), systemic infections by either Ustilago striiformis (stripe smut) or Urocystis agropyri (flag smut) have led to greater mortality under drought (Nus & Hodges, 1985); also, in maize infected by Ustilago maydis , smut severity was higher under stress, especially when the water deficit occurred at the grain‐filling stage (Kostandi & Soliman, 1998). We hypothesize that susceptibility to smut increases when the plant is exposed to drought stress at the pegging time.…”