Studies were carried out to determine the types of fungi and their levels of infection in cottonseed and embryos obtained from five varieties of cotton at our location during the summer of 1992. Other objectives were to determine when and how various fungi infect whole cottonseed and embryos and to obtain typical seed-infecting fungi from embryos for later studies on seed deterioration. Fluffed locks of Acala 1517-88, Coker 320, Deltapine 50, TAMCOT HQ-95 and Paymaster HS-26 were obtained at two different times after boll opening (August 8 and October 22), and 200 acid-delinted seed and 200 embryos of each variety were surface sterilized in 2% sodium hypochlorite, containing 0.001% triton X-100 for 2 min. Seed and embryos were placed on PDA containing antibiotics for 7 to 10 days at 25 C. The fungi obtained on PDA were transferred to water agar containing carnation leaves, and the fungi were identified in about 7 days. Infections of the seed and embryos usually involved only one or two fungi.

Seed and embryos obtained within 24 hr after boll opening on August 8 contained very few fungi and were of extremely high quality when studied using the standard warm germination test and the cool germination test. Levels of fungal infection were similar in the five varieties, and an average of 3% of seed from these varieties and 2.6% of their embryos were infected. Identical types of fungi were isolated from the seed and embryos. The fungi recovered from seed and embryos included Alternaria spp. (believed to be A. alternata), Aspergillus spp., Bipolaris sp., Cladosporium spp., Cunninghamella sp., Curvularia lunata, Exserohilum longirostratum, Fusarium chlamydosporum, F. semitectum, Nigrospora sp., Penicillium spp., Pestalotia sp. and various unidentified organisms.

Seed obtained from the five varieties October 22, nearly 10 weeks after the first sampling, were still high in quality but contained much higher levels of fungi than seed obtained within 24 hr after boll opening. The levels of fungi in embryos obtained from seed of these varieties were still low and had not changed appreciably from what they were near the time of boll opening. The percent fungal infection in whole seed of Acala 1517-88, Coker 320 Deltapine 50, TAMCOT HQ-95 and Paymaster HS-26 was 32, 45, 32, 68 an 22%, respectively. The percent fungal infection in embryos of Acala 1517-88 Coker 320, Deltapine 50, TAMCOT HQ-95 and Paymaster HS-26 was 3, 7 5, 3 and 4%, respectively. The most common fungi in seed of the five varieties were F. semitectum, F. Alternaria spp., and Cladosporium spp. The percent of F. semitectum, F. equiseti, Alternaria spp., an Cladosporium spp. in infected seed of Deltapine 50 was 65.0, 12.0, 14.7 an 4.0, respectively. These fungi were present in similar frequencies in seed of the other four varieties.

The five varieties were prematurely shredded and deep-plowed before more weathered seed could be obtained; older weathered seed of Deltapine 16, however, were obtained from a nearby plot. These seed were harvested on December 18, nearly four months after boll opening. They had a cool-warm vigor index of 153, suggesting they were still of good quality. Their ability to germinate and produce healthy seedlings at 18 C, however, was much less than for seed of the other five varieties, which were obtained earlier. The percent of fungi in seed and embryos of Deltapine-16 was 97 and 38%, respectively. The percent of F. semitectum, F. equiseti, Alternaria spp., and Cladosporium spp. in whole seed of Deltapine 16 was 30.0, 4.5, 8.1, and 49.3, respectively. The percent of E. semitectum, F. equiseti, Alternaria spp., and Cladosporium spp. in embryos was 36.5, 5.9, 3.5, and 38.8%, respectively.

These studies indicate that limited fungal invasion of seed and embryos took place during boll opening and increased during the period of field exposure. Infections of whole seed and embryos increased with time and it seems apparent that declining weather conditions in the months of October, November and December were critical in affecting seed deterioration and fungal infection of embryos.