Title: Pea germplasm with partial resistance to sclerotinia sclerotiorum that extends the time required by the pathogen to infect host tissue Author
Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 13, 2011
Publication Date: May 1, 2012
Citation: Porter, L. 2012. Pea germplasm with partial resistance to sclerotinia sclerotiorum that extends the time required by the pathogen to infect host tissue. Crop Science. 52:1044-1050. Interpretive Summary: Often times plant pathologist or breeders searching for resistance to specific pathogens screen through all available plant material of a crop for genes conferring complete resistance to the pathogen, but none are found. Presently pea breeders are facing the absence of pea lines with complete resistance to a fungal disease called white mold that can rot all parts of a pea plant. When no sources of resistance are found, often partial resistance to the pathogen is the only alternative breeders can use to try to improve disease resistance. Types of partial resistance can include reducing the size or rate that a lesion spreads, or reducing the spore production of a pathogen so it does not spread as easily. An additional type of partial resistance is identifying plants that increase the length of time the pathogen requires to infect the host tissue under environmental conditions favourable for infection. All of the wild and cultivated pea lines tested to date are susceptible to infection by white mold, but according to the present study, these lines can vary in the length of time required for infection or severe infection to take place, with severe infection being defined as an infection that prevents the plant from yielding. If a plant can prolong the time necessary for infection to take place, environmental conditions may change, resulting in avoidance of infection or severe infection. In the present study, selective wild pea lines and cultivars were assessed for the time required by the white mold pathogen to severely infect these varieties at all combinations of five temperatures (15.6, 18.3, 21.1, 23.9, 29.4ºC) and four (12, 24, 48 and 72 h) periods of high relative humidity (PHRH). Commercial pea cultivars tested did not prevent severe infection at any temperature/PHRH combination. However, several wild pea lines were identified that extended the time required for serious infection to take place at certain temperatures. Wild pea lines PI169603 and PI240515 are recommended to pea breeders as the best wild pea lines to use in breeding to improve this type of resistance.
Technical Abstract: White mold, caused by the fungus S. sclerotiorum can be a serious disease on pea. Currently there are no pea genotypes with complete resistance to this pathogen. Selective wild pea genotypes from the Pisum Core Collection and cultivars were assessed for the time required by S. sclerotiorum to severely infect these genotypes at all combinations of five temperatures (15.6, 18.3, 21.1, 23.9, 29.4ºC) and four (12, 24, 48 and 72 h) periods of high relative humidity (PHRH). Severe infection is defined as the death of all plant tissue above a stem inoculation point, preventing reproduction. Incorporation of genes into cultivars that increase the time required for severe infection to develop would improve disease avoidance if environmental conditions change from conducive to non-conducive for disease development. Commercial genotypes did not prevent severe infection at any temperature/PHRH combination. However, wild pea genotypes PI164972, PI169603, PI197044, PI240515, PI270536, and PI280611 prevented severe infection at temperatures of 15.6, 18.3, 29.4 and either 21.1 or 23.9 ºC, following a 12-h PHRH in repeated trials. PI164972, PI169603 and PI280611 also prevented severe infection following a 24-h PHRH, but only at 29.4 ºC. Severe infection occurred for all genotypes after a 48 or 72-h PHRH at all temperatures tested. PI169603 and PI240515 are recommended to pea breeders as the best germplasm to extend the time required for serious infection by S. sclerotiorum.