Selection for Resistance to Leptosphaerulina Leaf Spot in Alfalfa

Significant differences were observed among 11 alfalfa cultivars for the percentage of plants resitant to Leptospbaerulina briosiana after one inoculation. Screening for resistance was done by inoculating 18 day old plants (cv. Europe), held in a moist chamber, with L. briosiana. The self- and cross-progenies of plants resistant to L. briosiana after two inoculations showed slightly higher resistance to Leptosphaerulina leaf spot than the unselected original population but the difference was significant for the cross-progeny only. Larger variations were observed among self-progenies than cross-progenies. No correlation was found between self - and cross-progenies. At least three inoculations may be necessary to eliminate most susceptible plants. Mas selection was as effective as the polycross progeny test to improve the level of resistance of the selected populations as compared with the unselected one but the difference was agronomically unimportant. Under field conditions, the plants selected as resistant after two inoculations in the laboratory showed better resistance to L. briosiana than the susceptible ones but only on the first of three notations. The population derived from plants selected from cv. Europe as resistant to L. briosiana in the laboratory was not significantly more resitant than cv. Europe in the filed but generally showed less foliar infection.