Effects of Drought-Stress on <i>Fusarium</i> Crown Rot Development in Barley

<div><p><i>Fusarium</i> crown rot (FCR), caused by various <i>Fusarium</i> species, is a chronic disease of cereals in many semi-arid regions worldwide. To clarify what effects drought-stress may have on FCR development, visual assessment, histological analysis and quantitative PCR were used to analyse the infection process of <i>F</i>. <i>pseudograminearum</i> in barley. This study observed for the first time that the severity of FCR symptom reflects the quantity of pathogens in infected tissues of barley under both drought-stressed and well-watered conditions. Drought-stress prolongs the initial infection phase but enhances the proliferation and spread of <i>Fusarium</i> pathogens after the initial infection phase. Under drought-stressed conditions, the invading hyphae were frequently observed to re-emerge from stomata and invade again the surrounding epidermis cells. Under the well-watered conditions, however, very few hyphae re-emerged from stomata and most infection was caused by hyphae intracellularly grown. It was also observed that drought-stress increased the length and density of trichomes dramatically especially in the susceptible genotypes, and that the length and density of trichomes were positively related to fungal biomass of <i>F</i>. <i>pseudograminearum</i> in plants.</p></div

Effects of drought on trichome traits measured on drought-stressed and well-watered seedlings at 14 days post inoculation.

<p>Effects of drought on trichome traits measured on drought-stressed and well-watered seedlings at 14 days post inoculation.</p

Effects of Drought-Stress on <i>Fusarium</i> Crown Rot Development in Barley - Fig 3

<p><b>The infection and colonization of barley coleoptile by <i>Fusarium pseudograminearum</i></b> A: Small amounts of hyphae emerging from stomata and re-invading the surrounding epidermis cells at 3 dpi in the drought-stressed genotype Fleet. B: Intracellular invasive hyphae growing in epidermis cell adjacent to stomata at 3 dpi in the well-watered genotype Fleet. C: Surface mycelium growing through heavily infected tissue at 7 dpi in the drought-stressed genotype Franklin. D: Intracellular hyphae growing within epidermal cells at 7 dpi in the well-watered genotype Franklin. (Tissues were stained using Fluorescent brightener 28 and viewed under ultraviolet light.) S: stomata; L: lesion; IH: intracellular hyphae; SM: surface mycelium.</p

Showing typical difference in <i>Fusarium</i> crown rot severity between drought-stressed (left) and well-watered seedlings (right) of the susceptible barley genotype Fleet at 21 days post inoculation.

<p>L1: the first leaf sheath; L2: the second leaf sheath.</p

<i>Fusarium pseudograminearum</i> colonization of barley leaf sheath tissues.

<p>A: A mass of surface mycelium entering the open stoma at the base of heavily infected second leaf sheath at 28 dpi in the drought-stressed genotype Franklin. B: Intracellular hyphae growing within epidermal cells at the base of heavily infected second leaf sheath tissues at 28 dpi in the well-watered genotype Franklin. C: Large quantity of surface mycelium occurred around trichomes at 28 dpi in the first leaf sheath of the drought-stressed seedling of Fleet. D: A small amount of mycelium appeared around trichomes at 28 dpi in the first leaf sheath of the well-watered genotype Fleet. E: Large quantity of hyphae re-emerging from stoma at 28 dpi in the first leaf sheath of the drought-stressed genotype Fleet. F: Small quantity of hyphae re-emerging from stomata and a large quantity of intracellular hyphae growing within and across epidermal cells at 28 dpi in the first leaf sheath of the well-watered genotype Fleet. (Tissues were stained using Fluorescent brightener 28 and viewed under ultraviolet light.) S: stomata; L: lesion; IH: intracellular hyphae; SM: surface mycelium; T:trichome.</p

Relative <i>Fusarium pseudograminearum</i> biomass obtained by real-time quantitative PCR at different time points during <i>Fusarium</i> crown rot infection and development.

<p>DS: drought-stressed treatment; WW: well-watered treatment.</p

QTL for FCR severity, plant height and heading date identified in the population of EGA Wylie/Sumai3^#_.

#<p>The three trials conducted for assessing FCR severity were designated as FCR-01, FCR-02 and FCR-03, respectively; the two trials conducted for estimating plant height were designated as PH-01 and PH-02, respectively; and the two trials conducted for estimating heading date were designated as HD-01 and HD-02, respectively. IM = interval mapping; and MQM = QTL detection with a multiple QTL model.</p

Effects of QTL conferring FCR resistance in the two validation populations^#_.

#<p>‘RR’ represents homozygous alleles from the resistant parent EGA Wylie, and ‘rr’ those from non-' EGA Wylie' parents.</p

Disease index (DI) of Fusarium crown rot (FCR) and plant height in the population EGA Wylie/Sumai3^#_.

#<p>The three trials conducted for assessing FCR severity were designated as FCR-01, FCR-02, and FCR-03, respectively; and the two trials conducted for estimating plant height (PH) were designated as PH-01 and PH-02, respectively.</p

QTL conferring FCR resistance detected with interval mapping (IM) on chromosome arm 2DL in the population of EGA Wylie/Sumai3.

<p>The LOD values from each centimorgan of the chromosome were plotted against the chromosome, and the threshold LOD value (2.9) based on permutation test for declaring the presence of a QTL was indicated by a dotted line.</p