Mycofloral Succession and Viability Losses in Pigeon pea Seed in Puerto Rico

Abstract

Using the cellulose pad and potato dextrose agar (PDA) assays, twenty three fungi were found on pigeonpea seed in Puerto Rico. In the PDA assay, Botryodiplodia theobromae was the most common (29%). On cellulose pads, the same fungus was not very common (7%). PDA assay favored increased detection of Alternaria tenuissima, Phomopsis sp., and total fungi compared with cellulose pads. Cellulose pads favored detection of Cladosporium sp. In both assays, incidences of B. theobromae, Fusarium spp., and total fungi were negatively correlated with seed germination. Measurements for seedlot germination were highly correlated (r = 0.77**) between the two assays. The influences of seed type and delayed harvest on pigeonpea seed viability were studied. Pigeonpeas "28-Bushy," with large tan seeds, showed reduced seed viability and higher incidence of B. theobromae and Fusarium spp. compared with segregants of the same cultivar with small flattened hard red seed. A 3-week delayed harvest drastically increased incidence of B. theobromae, Fusarium spp., and total fungi, and reduced germination in "Kaki" pigeonpeas from Santa Isabel. Pigeonpea seed viability and mycoflora were followed before and after farm storage. Incidences of Fusarium spp., Phomopsis sp., Cladosporium sp., and B. theobromae after storage were 15, 26, 30, and 38% of their respective prestorage values. Incidence of species of Penicillium, Rhizopus, and Aspergillus increased during storage. Although less than 3% Aspergillus spp. was detected in the cellulose pad assay at 27° C, 28 to 92% was detected when seed were incubated at 35° C using pigeonpea seed extract in 2% agar. With the Aspergillus selective assay, seed viability losses during storage were highly correlated with incidence of Aspergillus spp. (r = 0.96**). Aspergillus incidence in the cellulose pad assay was not associated with storage losses in seed germination (r = 0.18 NS). Emergence and fungal colonization of pigeonpea seed were dependent on soil moisture. Pigeonpea seed did not emerge at either 25 or 100% soil moisture holding capacity (SMHC). Optimum emergence was found at 50% SMHC. Pythiaceous fungi were predominent on seed at and above 75% SMHC, whereas Aspergillus spp. predominated at 50% SMHC or less. Mixed populations of the two were visible at 50 and 75% SMHC.