Measurement of Resistance to Fusarium Wilt/Root and Crown Rot in Birdsfoot Trefoil Populations
- K. E. Zeiders and
- R. R. Hill
Fusarium wilt disease [caused by Fusarium oxysporum (Schlect) Snyd. & Hans.] has been identified as an important factor in stand decline in birdsfoot trefoil (Lotus corniculatus L.) seed production fields in the Champlain Valley of New York and Vermont. In response to this problem, studies to develop resistance to F. oxysporum were initiated. In greenhouse inoculations tests, two broad-based populations of birdsfoot trefoil were subjected to two cycles of recurrent phenotypic selection for resistance to wilt/root and crown rot caused by F. oxysporum. In a cycle comparison test, plants were rated for disease severity four times at 30-d intervals after inoculation. The objectives were to evaluate the effectiveness of selection and to compare different methods of measuring resistance to the pathogen. Disease resistance was measured by: (i) disease progress curves based on visual wilting/stunting ratings of individual plants (DSW); (ii) frequencies of plants rated > 2 (DSD) (where 1 = no disease to 5 = plant dead), indicating moderate or greater wilting/stunting; (iii) area under the disease progress curve (AUDPC) calculated from curves in method ii; and (iv) root and crown rot ratings (RCR) of individual plants at the end of the experiment. Analyses by each of the four measures of resistance indicated that recurrent selection increased resistance to F. oxysporum in birdsfoot trefoil. Cycle 0 plants of each population were among the most susceptible, and Cycle 2 plants were among the most resistant of all entries in the evaluation test. Analyses of DSW and DS2 indicated similar responses to selection. Disease severity increased until Day 90 of the test with little or no increase thereafter. Analysis of AUDPC was more sensitive to larger increases in disease severity early in the evaluation trial. Analysis of RCR ratings indicated less progress from selection than with the other measures of resistance.
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