Sobero y Rojo
Depto. de Tecnología, Universidad Nacional de Luján, CC No. 221, 6700 Luján, Buenos Aires, Argentina
C.I.C., Fac. Ciencias Agrarias, Universidad Nacional de La Plata, Av. 60 y 119, 1900 La Plata, Argentina; E-mail: <email@example.com>
Soybean (Glycine max) is an important crop in the northern area of the province of Buenos Aires, Argentina. Phomopsis spp. and Fusarium spp. are the prevalent pathogens in soybean seeds. Infection levels for both pathogens can be greater than 50%. In seedlings growing in sand or soil, both pathogens produce rotten lesions on cotyledons and hypocotyls, but over the past 2 years a plumele soft rot has also been observed associated with detached teguments that was previously demonstrated to be caused by Fusarium spp. (1). In 1996, seeds with a germination level lower than 82% were selected from an assay including 22 cultivars, and examined for the presence of Fusarium spp. The infection level ranged from 2 to 16%, and the Fusarium spp. present were identified as F. equiseti, F. oxysporum, and F. pallidoroseum. After each Fusarium sp. was cultured on potato dextrose agar, a conidial suspension was prepared and adjusted to 1.8 × 106 conidia per ml. This inoculum was sprayed on water-soaked paper, in petri dishes, and good quality soybean seeds were placed on the paper, with 400 seed for each Fusarium sp. The petri dishes were maintained at 26°C for 24 h. Control seeds were plated on water-soaked paper. Inoculated seeds were sown in sand with a water content of 16% wt/wt, covered with polyethylene bags, and incubated for 7 days in a growth chamber at 26°C and a 12-h light period. All the samples inoculated with the three Fusarium spp. exhibited seed rot, seedlings with cotyledon and hypocotyl lesions as described previously (2), but also plumele soft rot. Control seedlings remained symptomless. This is the first report confirming that the characteristic plumele soft rot of soybean seedlings is a nonspecific symptom associated with F. equiseti, F. oxysporum, and F. pallidoroseum.
References: (1) B. González et al. ISTA-PDC Symp., 2nd. 1996. (2) G. S. Saharan and V. K. Gupta. Plant Dis. Rep. 56:693, 1972.