CIC, Laboratorio de Fitopatología, Fac. Cs. Agrarias y Forestales, UNLP, 60 y 119, 1900 La Plata, Buenos Aires, Argentina; E-mail: <email@example.com>
During the summer of 1995-1996, an 80-ha field of 6-year-old asparagus plants (cv. UC 72) in Saladillo (Province of Buenos Aires) was affected by a decline syndrome (1). The plants showed a decline in vigor and approximately 60 to 70% of the plants died. The symptomatic plants were chlorotic, stunted, with stem lesions and crown and root rot. Fusarium moniliforme and F. proliferatum were isolated from vascular and epidermal tissues of roots, crowns, and stems. Identification of Fusarium to species was made by examining conidiogenous cells from colonies cultured on KCl medium (2). Microconidia were born in long and short chains and false heads. The isolates were identified based on the the presence of polyphialides in F. proliferatum and their absence in F. moniliforme, which produces monophialides only (2). In two separate trials, asparagus seeds (cv. UC 72) were surface sterilized and placed in steamed soil infested with a conidial suspension of each species. The viable propagules in the soil (CFU per g) were estimated by soil plate dilutions on Nash & Snyder-PCNB (pentachloronitrobenzene) medium. The F. moniliforme and F. proliferatum soil densities were 19.2 × 103 and 23 × 103 CFU per g of soil, respectively. The pots were placed in the greenhouse on different benches to avoid cross-contamination. After 4 months, inoculated plants showed root and crown discoloration. F. moniliforme and F. proliferatum were reisolated (64 and 75%, respectively) from discolored portions of internal and external root and crown tissues. Although the stems did not show symptoms, F. moniliforme and F. proliferatum were also recovered (27 and 38%, respectively) from asymptomatic tissues. Six months after inoculation the plants developed chlorotic symptoms with crown and root rot, and then wilted. F. moniliforme and F. proliferatum were reisolated from root systems, crowns, and stems of all inoculated plants. F. moniliforme and F. proliferatum are involved in corn stalk and ear rot in Argentina. Corn and asparagus are frequently grown in close proximity and often follow one another at a particular site. Airborne and soil debris carrying F. moniliforme and F proliferatum from corn may be an additional source of inoculum for asparagus in Argentina. The results indicate that the presence of F. moniliforme and F. proliferatum is a factor that contributes to asparagus decline in Argentina.
References: (1) W. H. Elmer et al. Plant Dis. 80:117, 1996. (2) P. E. Nelson et al. Fusarium Species: An Illustrated Manual for Identification. Pennsylvania State University, University Park, 1983.