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Screening for Resistance to Rotylenchulus reniformis in Soybean: Correlation Analysis of Assessment Parameters and Varietal Response to This Nematode and Meloidogyne incognita
Abstract:
The study was designed to search for resistance of soybean to R. reniformsis, to correlate the parameters used in determining the host categories, and to compare the interactions of soybean varieties with different degrees of resistance to this nematode and to M. incognita.
Based on resistance ratings or averages of computed indices for root necrosis, nematode recoveries of roots and soil, and numbers of egg masses and eggs per mass, 9, 13, 26 and 26 soybean varieties were found to be resistant, moderately resistant. moderately suscptible, respectively, to R. reniformis in a field screening.
Highly significant positive linear correlations were found between resistance rating and any one of the assessment parameters used, with nematode recovery from roots, total recoveries from root and soil and necrosis rating appearing to be the most species.
Earlier root penetration and gall formation by M. incognita, faster nematode development and higher recoveries were also assoiciated with susceptibility. Nematode life cycle was completed in 43 to 47 days after penetration in susceptible varieties but one occured in resistant varieties within 53 days from penetration. Penetration by R. reniformis, development to egg-laying stage and apperance of root necrosis occured simultaneously in both susceptible and moderatly susceptible varieties, but were delayed in the resistant ones. Life cycle was completed in 14 to 18 days 19 to 23 days after penetration in susceptible and moderately susceptible varieties, respectively, while none occured in resistant varieties in 21 to 22 days from penetration.