Stability of resistance to Phytophthora infestans in potato: an international evaluation

Abstract

Ten institutions in nine countries joined together to test the stability of resistance of 14 potato genotypes to the oomycete pathogen Phytophthora infestans in three separate trials. Seven of the genotypes were tested in one trial involving seven locations, and all 14 were tested in two subsequent trials, each involving eight locations. Stability of resistance was tested with nonparametric tests and with an additive main effects and multiplicative interaction (AMMI) model. Overall, resistance to P. infestans was robust; resistant genotypes were consistently resistant in all locations and trials. The nonparametric analysis indicated that specific genotypes were basically stable across sites for resistance. In trial 3, the Z statistic for overall stability was significant at 0·05%, indicating a significant level of interaction across the trial, but there were no significant interactions for specific genotypes in this trial. The genotype by environment (G × E) effect of the AMMI model was highly significant in both trials, but the mean square of G × E was less than 10% of the genotype effect in each trial. The first two principal components (PCA1 and PCA2) of the AMMI analyses together explained 75 and 80% of the interaction effects in trials 2 and 3, respectively. Based on both nonparametric and AMMI analyses, Ecuador and Argentina were locations of relatively high interaction effects for both trials 2 and 3, although in Ecuador this interaction was not associated with any particular potato genotype. Other locations also had high interaction effects, but these occurred in only one trial. The genotypes Chata Blanca and, to a lesser extent, Torridon were relatively unstable in trials 2 and 3, but in the case of Torridon, resistant, this did not represent a significant loss of resistance.

The field resistance of potato cultivars to foliar late blight and its relationship with foliage maturity type and skin type in Brazil

“…Whenever potato resistance instability is detected, it may be due to three factors: the environment, the pathogen population or a combination of these (Forbes et al 2005). Instability in certain cultivars was observed.…”

“…The cultivar Alpha was more resistant in New York State than in Vale da Toluca (Mexico), and three other genotypes behaved similarly in both locations (Parker et al 1992). The Atzimba cultivar presented a moderate level of resistance to foliar late blight in Mexico but was considered susceptible in Costa Rica (Forbes et al 2005). This illustrates that the levels of resistance of potato cultivars may vary from one location to another.…”

“…The variables used to identify potato cultivar resistance to foliar late blight in the present trials are the same as those used by a number of other authors, including the area under the disease progress curve (Cadena-Hinojosa et al 2007;Flier et al 2003;Forbes et al 2005;Fry 1978;Grünwald et al 2000;Hansen et al 2005;Haynes and Weingartner 2004;Ojiambo et al 2000), the rate of disease progress (Fry 1978;Ojiambo et al 2000), the maximum disease severity (Cadena-Hinojosa et al 2007;Fry 1978;), the yield data (Cadena-Hinojosa et al 2007) and the number of epidemic days (Hansen et al 2005). In these papers, variables were analyzed individually over time, but in the present work all of the variables were simultaneously analyzed to obtain a more global and simplified interpretation.…”

Host Specialization not Detected Among Isolates of the EC-1 Lineage of Phytophthora infestans Attacking Wild and Cultivated Potatoes in Peru

“…Wild tuber-bearing potatoes from central and south America have been used as the primary sources of resistance to P. infestans (Glendinning, 1983;van Soest et al, 1984;RiveraPen˜a, 1990;Colon et al, 1995a;Trognitz et al, 2002). Several studies have recently demonstrated the geographic (Haynes et al, 1998;Forbes et al, 2005) and temporal (Colon et al, 1995b;Gru¨n-wald et al, 2002a) stability of quantitative resistance, which can result in significant reductions in fungicide use (Gru¨nwald et al, 2002b).…”

Phenotypic Expression of Resistance to Phytophthora infestans in Processing Potatoes in Argentina

“…One potential concern associated with the evaluation of susceptibility in potato to P. infestans is the potential for a host-by-location interaction that may be due to several factors, including poor host adaptation in some locations (Forbes et al 2005) and race-specific interactions (Andrivon et al 2006). Race-specific interactions have also been detected for putative quantitatively inherited resistance (Flier et al 2003).…”