Viability ofPhakopsora pachyrhiziUrediniospores Under Simulated Southern Louisiana Winter Temperature Conditions

Abstract

Soybean rust, caused by Phakopsora pachyrhizi, originally occurred in Asia. It has now spread to South America and the continental United States. This disease has the potential to cause severe economic losses to U.S. soybean growers, especially in the south, where the environmental conditions are more favorable to P. pachyrhizi survival during winter. In the present study, the effect of simulated southern Louisiana winter temperature conditions (12°C, 14-h days and 1°C, 10-h nights with 75% relative humidity) on soybean rust urediniospore viability was examined. It was found that urediniospore viability declined rapidly from 72 to 40% after 1 day and then decreased gradually to 17% after 7 days and 11% after 60 days. Spores stored under southern Louisiana winter conditions for 60 days still produced pustules on inoculated leaves. In comparison, the viability of spores stored at room temperature decreased gradually and reached 0% at the end of 60 days. Winter temperature treatment not only reduced spore viability but also decreased germ tube growth. In addition, soybean rust spores recovered from overwintered dry kudzu leaves were also found viable. This study indicates that soybean rust spores could survive southern Louisiana winter conditions and initiate a new cycle of infection in the next growing season.

CulturingPhakopsora pachyrhizion Detached Leaves and Urediniospore Survival at Different Temperatures and Relative Humidities

“…pachyrhizi was first reported from the continental Unites States in 2004 in Louisiana (45), and has become established in the southern United States along the Gulf of Mexico, overwintering on kudzu (38). pachyrhizi was first reported from the continental Unites States in 2004 in Louisiana (45), and has become established in the southern United States along the Gulf of Mexico, overwintering on kudzu (38).…”

“…In vivo culturing of P. pachyrhizi on detached soybean leaves placed on agar-amended media (10,39,53) or on filter paper (38) inside petri dishes has been successful for maintaining leaf pieces to evaluate the host-pathogen interactions (10,39,54). Detached-leaf culturing has also been useful to study host-pathogen interactions for other rust fungi such as Puccinia coronata (24), Uromyces viciaefabae (18), P. sorghi (21), and non-rust pathogens Mycosphaerella fijiensis (55) and Phytophthora infestans (49).…”

GERMINATION AND INFECTION OF Phakopsora pachyrhizi UNDER SIMULATED ENVIRONMENT OF THE CENTRAL AREA OF SANTA FE, ARGENTINA

“…A urediniospore was considered completely germinated when the length of the germination hypha was at least as long as its largest diameter (Yorinori, 2004). Germination and viability of the urediniospores were evaluated at 6 and 18 hours post incubation and then every 2 days during the subsequent 10 incubation days according to Yang (2002) and Park et al (2008). From the composite sample assigned to each Treat.…”

“…The GU % was estimated as: (germinated urediniospore number / total number of urediniospores counted on 16 visual fields with 4 replications) x 100. Number of GU between evaluation times were recognized by staining of the active (alive) germinative hyphas with cotton blue (Furtado et al, 2008;Park et al, 2008).…”

A FERRUGEM ASIÁTICA DA SOJA CAUSADA POR Phakopsora pachyrhizi Sydow e Sydow

“…Segundo Reis et al (2006a), biotrófico é aquele parasita que depende nutricionalmente dos tecidos vivos do hospedeiro, ou seja, da célula viva, de onde extraem os nutrientes essenciais a suas atividades vitais, apresentando assim menor número de oportunidades ou mecanismos para sobrevivência do que os necrotróficos. Reis et al (2006a), Park et al (2008) e Slaminko et al (2008) indicam que uredosporos de P. pachyrhizi podem sobreviver no inverno de uma safra para outra em plantas de kudzú (Pueraria lobata), as quais servem de fonte de inóculo. Os esporos secos do fungo são disseminados pelo vento (Maude, 1996) ou por outros meios, como pessoas (Hartman e Haudenshield, 2009).…”