Stem‐Tip Inoculation of Alfalfa with Sclerotinia trifoliorum: I. Development of Necrosis on Resistant and Susceptible Selections

Abstract

A stem-tip inoculation procedure has been successfully used in divergent selection for resistance to Sclerotinia trifoliorum (Eriks) on alfalfa (Medicago saliva L.). One unreported observation made in early studies was that lesion development was not continuous for some alfalfa plants over the 14-d incubation. A more in-depth study of disease development was needed to quantify the variability, and the stem-tip inoculation procedure was modified for this purpose. Inoculated stems were placed in plastic sleeves and marks were made daily on the plastic to show the development of necrosis over time. Eight plants previously selected for their higher levels of resistance and eight plants selected for minimal resistance (susceptibility) developed necrosis after 14 d in the plastic sleeves, which was similar to that measured in earlier studies. The length of the lesion on susceptible plants was described by a linear equation with 0.9 to 1.3 cm of necrosis d i. Six of the resistant plants stopped the lengthening of the necrotic stem lesion about 8 d after inoculation while two of the resistant selections continued linear development at rates much less than that measured on the susceptible selections. When the necrotic region stopped developing, a dark border usually developed between the green and necrotic tissues which was not seen when disease continued to develop. Statistical analysis suggested disease resistance might be effected by either of two qualitatively different systems.

Resistance of lucerne (<i>Medicago</i> spp.) germinating seeds to oxalic acid

“…If seeds are highly deficient or only several plants are available, other methods for OA application are available. Excised leaf tissues [29] and stem-tip methods [21,30] could be used for testing a limited number of plants.…”

Evaluation of faba beans for resistance to sclerotinia stem rot caused by Sclerotinia trifoliorum

“…It is considered a major disease of many important crops such as dry bean (Phaseolus vulgaris L.), soybean (Glycine max L.), alfalfa (Medicago sativa L.), and many other legumes (Delclos et al 1997;Halimi and Rowe 1998;Kim et al 2000;Steadman et al 1997). This disease is often a serious problem of faba beans (Vicia faba L.) in Greece (Roupakias 1983) caused by the fungus Sclerotinia trifoliorum Eriks.…”

“…Several studies, using different evaluation methods under controlled conditions, indicated measurable genetic differences in the levels of resistance to S. trifoliorum in alfalfa (Halimi and Rowe 1998;Pierson et al 1997;Pratt and Rowe 1994;Rowe and Welty 1984) and red clover (Trifolium pratense L.) (Delclos et al 1997). Similar data were reported for a closely related disease caused by Sclerotinia sclerotiorum (Lib.)…”