Alternative hosts of Phakopsora pachyrhizi in the Americas: an analysis of their role in the epidemiology of Asian soybean rust in the continental U.S.
Role of susceptible hosts of Phakopsora pachyrhizi in the occurrence of epidemics of Asian soybean rust (ASR) in the U.S. was assessed. Phenology of kudzu (Pueraria montana var. lobata) along a ∼800 km transect in the U.S. was characterized in 2003 and 2004 to assess the potential for kudzu to serve as an inoculum source for occurrence of ASR and subsequent spread to the north central soybean growing regions. Also, the occurrence, distribution, and growing periods of six potential hosts of P. pachyrhizi (including kudzu and soybean), in Central America, the Caribbean, and Mexico, were delineated. Sampling data revealed that bud break of kudzu plants in the two consecutive years of study occurred as early as April 7 from southern Louisiana (29.8 N latitude) to northern Mississippi (35.0 N latitude); kudzu green leaf area index decreased linearly with increasingly northern latitude (R2 and regression coefficient = 0.750 & --0.097, respectively, for 2003 and 0.654 & --0.384 for 2004). Further, results of modeling predicted that in southern Mississippi (31.5 N latitude), kudzu plants broke dormancy in the second and first week of March in 2003 and 2004, respectively. Modeling also showed that kudzu vines may break dormancy prior to March 1st in areas of southern and central Florida and southern Louisiana. Amount of kudzu foliage increased abruptly from April to May and June. Five out of the six hosts investigated in Central America, the Caribbean, and Mexico, were found to occur in such regions. Occurrence of selected hosts in each region was documented and maps of distribution and cultivation period schemes were generated.