Effect of temperature on spore viability of Neonectria ditissima

The fungus Neonectria ditissima causes European canker on apple and pear trees in temperate regions The thermal death point of ascospores and conidia of this pathogen is unknown In this study ascospores and conidia were exposed to six temperatures between 20C and 50C for seven time intervals between 5 min and 24 h The viability of the spore suspensions was determined by germination on slides and growth on potato dextrose agar Temperatures up to 30C did not reduce spore viability Exposure to 35C for 24 h reduced conidial and ascospore germination by 92 and 85 respectively At 40C and 45C spore viability was reduced after 5 min declining rapidly with increasing exposure times No spores germinated after 5 min at 50C This study suggests that 15 min dips in 45C water may kill surface spore contamination of budwood prior to grafting Budwoodbased validation studies are now recommended

Relationship between Temperature and Heat Duration on Large Crabgrass (Digitaria sanguinalis), Virginia Buttonweed (Diodia virginiana), and Cock's-Comb Kyllinga (Kyllinga squamulata) Seed Mortality

Thermal heat has been utilized for nonselective weed control methods. These methods are highly variable in application and efficacy. One effective weed–seed-control determining factor is achieving the thermal death point of targeted weed seeds. The thermal death point varies by weed species, temperature, and exposure time. Our objective was to determine the thermal death point of large crabgrass, cock's-comb kyllinga, and Virginia buttonweed at short thermal exposure periods. Studies conducted utilized 5 and 20 s exposure periods for incremental range, 60 to 250 C temperatures. Sigmoid regression curves were used to predict weed seed mortality by temperature and exposure time. A significant interaction between exposure period and temperature occurred for each weed species. Weed species increased in susceptibility to 20 s thermal heat as follows: Virginia buttonweed < cock's-comb kyllinga < large crabgrass. Increasing thermal exposure time from 5 to 20 s reduced thermal temperature by 21 C to achieve 50% mortality for large crabgrass and by 10 C for cock's-comb kyllinga. Virginia buttonweed achieved 50% mortality at 99 C for 5 and 20 s exposure periods. These data indicate that at least 50% weed seed mortality can be achieved at 99 and 103 C for 20 and 5 s exposure periods, respectively, for these weed species.

Time and temperature combinations that are lethal to Pseudomonas syringae pv actinidiae

The thermal death point was determined in vitro for three isolates of Pseudomonas syringae pv actinidiae (Psa) A bacterial suspension was treated by placing in an Eppendorf tube then floating in a water bath at seven temperatures from 263 to 60C At each temperature an aliquot was removed after 5 15 35 75 155 315 and 635 min placed onto Kings medium B (KMB) in Petri plates and spread with a sterilised bent glass rod Petri plates were placed at 25C for 24 h and colonies counted There were three isolate replicates each in an Eppendorf tube per timetemperature combination There was no difference in response between isolate replicates but time and temperature differences were significant (P

Microflora of heat-damaged rapeseed

Microfloral components present on two sound lots (1 and 2) and three sample grade, heat-damaged lots (3 to 5) of stored Canadian rapeseed (Brassica campestris L. and B. napus L.) were determined with and without surface disinfection. Lots 1 and 2 were from a granary and a warehouse, respectively, and lots 3 to 5 were from primary elevators. Seed in lots 4, 5, and 3 showed progressively increased effects of heat damage as shown by the crush test. Sound lots 1 and 2 had mainly Alternaria and Cladosporium spp. with traces of Eurotium amstelodami, E. repens, and Penicillium spp. Lot 4 seed had low–medium levels of Alternaria alternata, Absidia ramosa, E. amstelodami, and Mucor pusillus. Lot 5 had high levels of E. amstelodami and low levels of Talaromyces thermophilus but A. alternata and M. pusillus were largely absent. Lot 3 had deeper-seated E. amstelodami, T. thermophilus, and Penicillium spp. than lots 4 and 5. Eurotium amstelodami was the predominant storage fungus in the heat-damaged lots. During the early stages of heating, E. amstelodami was often accompanied by the primary sugar fungi M. pusillus and A. ramosa, and after severe heating, by T. thermophilus. The thermal death point was between 50 and 60 °C for moist seed and between 80 and 90 °C for dry seed after 30-min exposure. With the exception of E. amstelodami, heat resistance of the fungal flora did not exceed that of the seed.