Foliar Resistance to Phytophthora infestans (Mont.) de Bary (US-8) in 13 Mexican and South American Solanum Species Having EBNs of 1, 2, and 4 and Implications for Breeding

American Journal of Potato Research, Nov/Dec 2004 by Zlesak, David C, Thill, Christian A

ABSTRACT

The recent US-8 clonal lineage of Phytophthora infestans, the pathogen causing late blight (LB) disease, is one of the most widespread and difficult to control. Sources of foliar resistance to US-8 were evaluated in 1927 seedling genotypes by sampling 49 plant introductions (PIs) representing 13 Mexican and South American Solarium species having an Endosperm Balance Number (EBN) of 1, 2, or 4, and one species with an unknown EBN. Species evaluated were 2x(1EBN) S. bulbocastanum, S. cardiophyllum, S. commersonii, S. pinnatisectum, and S. trifidum; 2x(2EBN) S. berthaultii, S. megistacrolobum, S. microdontum, and S. verrucosum; 4x(2EBN) S. fendleri and S. stoloniferum; 6x(4EBN) S. guerreroense; 2x unknown EBN S. polyadenium; as well as 4x S. tuberosum families as controls. Foliar resistance in the field was monitored in 1998 and 1999. Resistance differed relative to species geographic origin, EBN, species themselves, PIs within a species, and genotypes within a PI. In 1998 Mexican germplasm had a lower area under the disease progress curve (AUDPC, 1140) and greater resistance than South American germplasm (1601), while the 1EBN (1119) and unknown EBN (1075) species had greater resistance than 2EBN (1470) and 4EBN (1888) species. AUDPC ranged among species from 555 (S. cardiophyllum) to 1932 (S. megistacrolobum) and among PIs within a species most widely for S. bulbocastanum (267-1007) and least widely for S. polyadenium (1019-1179). In 1999 LB symptoms were not observed on the species before an early freeze; however, all 1999 S. tuberosum families showed LB symptoms and segregated for resistance, pointing to greater resistance in the species than in cultivated germplasm. Resistance found in diploid 2EBN germplasm is more accessible due to greater crossability with cultivated germplasm; however, though more difficult to introgress, resistance found in some of the more reproductively isolated IEBN germplasm is worth pursuing.

Accepted for publication 10 August 2004.

ADDITIONAL KEY WORDS: Endosperm Balance Number, EBN, late blight, Phytophthora infestans, potato breeding, Solanum species

ABBREVIATIONS: AUDPC, area under the disease progress curve; EBN, Endosperm Balance Number; LB, late blight; NRSP-6, USDA/ARS Potato Introduction Station; PIs, plant introductions; UMORE, University of Minnesota, Outreach, Research and Extension Park

RESUMEN

El nuevo linaje clonal US-8 de Phytophthora infestans causante de la enfermedad conocida como tizón tardío (LB) es uno de los más difundidos y difícil de controlar. Se evaluaron las fuentes de resistencia foliar en 1927 genotipos de plántulas, muestreando 49 introducciones de plantas (PIs) que representan 13 especies de Solanum mexicanas y sudamericanas, con un número de balance del endospermo (EBN) de 1, 2, o 4 y una especie de EBN desconocido. Las especies evaluadas fueron 2x(1EBN) S. bulbocastanum, S. cardiophyllun, S. commersonii S. pinnatisectum y S. trifidum; 2x(2EBN) S. bertaulthii, S. megistacrolobum, S. microdontum y S. verrucosum; 4x(2EBN) S.fendleri y S. stoloniferum; 6x(4EBN) S. guerreroense; S. polyadenium 2x de EBN desconocido y familias de S. tuberosum 4x, fueron también incluidas como testigo. La resistencia foliar en el campo fue monitoreada en 1998 y 1999. La resistencia fue relativamente diferente en especies de origen geográfico distinto, EBN, especie, Pis dentro de la especie y genotipos dentro de un mismo PI. En 1998, el germoplasma mexicano presentó menor área bajo la curva de progreso de la enfermedad (AUDPC, 1140) y mayor resistencia que el germoplasma sudamericano (1601), mientras que el IEBN (1119) y la especie de EBN desconocido (1075) tuvieron mayor resistencia que las especies 2EBN (1470) y 4EBN (1888). El AUDPC varió entre especies de 555 (S. cardiophyllum) a 1932 (S. megistacrolobum) y entre PIs dentro de una especie, más amplio para S. bulbocastanum (267-1007) y más restringido para S. polyadenium (1019-1179). En 1999, no se observaron síntomas de LB en esta especie antes de la primera helada, sin embargo, todas las familias de S. tuberosum mostraron síntomas de LB y segregaron para resistencia, indicando mayor resistencia en la especie que en el germoplasma cultivado. La resistencia encontrada en el germoplasma diploide 2EBN es más accesible debido a una mayor posibilidad de cruzamiento con el germoplasma cultivado, sin embargo, aunque es más difícil la incorporación de genes por hibridación, vale la pena hacer un seguimiento de la resistencia hallada en el germoplasma 1EBN aislado de los cruzamientos más reproductivos.

INTRODUCTION

The potato disease late blight (LB), caused by the pathogen Phytophthora infestans, is one of the most important diseases that affects the potato industry worldwide. The disease reduces yield through rapid foliar destruction in the field as well as tuber decay during growth and development and during storage (Hooker 1981). Today both Al and A2 mating types of P. infestons exist worldwide. Since the first A2 collection in Europe (1981) (Hohl and Iselin 1984) and in the United States (1987) (Deahl et al. 1991), reports abound that the clonal lineages of A2 are displacing Al lineages in many areas (Goodwin et al. 1995, 1996; Koh et al. 1994; Marshall-Farrar et al. 1998; Platt 1994; Sujkowski et al. 1994). The US-8 (A2) clonal lineage is more virulent than the once predominant US-1 (A1) lineage and has displaced it in many growing regions within the United States and Canada (Fry and Goodwin 1997; Goodwin et al. 1995, 1996; Marshall-Farrar et al. 1998; Miller et al. 1998; Platt 1994). Compared to US-1, the US-8 has greater lesion-area expansion capacity (Kato et al. 1997; Miller et al. 1998) and greater tuber infection potential (Lambert and Currier 1997; Marshall and Stevenson 1996). In addition, US-8 and other recent clonal lineages are insensitive to metalaxyl, a once commonly used systemic fungicide that was effective in late blight control (Goodwin et al. 1996; Kato et al. 1997).