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Host-pathogen interactions of a new species of Phytophthora , causal agent of late blight of tree tomato ( Solanum betaceum Cav.), identified as Phytophthora betacei , were investigated with four different cultivars. Thirty-six P. betacei isolates, collected from southern Colombia between 2008 and 2009, were used to inoculate common tree tomato cultivars, Común, Híbrido, Injerto, and Holandés. Data on incubation and latent periods as well as infection efficiency, lesion development, and total sporulation were collected via detached leaf assays. Significant differences in susceptibility, based on the parameters measured, were observed. Común was the most susceptible cultivar, followed by Injerto, Híbrido, and Holandés. The mean incubation period was lowest for Común at 125.6 h post-inoculation (hpi) and highest for Híbrido at 139.4 hpi. No significant differences in latent period were observed. All 36 isolates produced necrotic lesions on Común, and 33, 24, and 21 caused infection on Injerto, Híbrido, and Holandés, respectively. Two isolates were able to cause infection only on Común, and 13 isolates were able to infect all four cultivars. Infection efficiency was significantly higher for the cultivar Común, followed by Injerto, Híbrido, and Holandés. Average lesion size was larger on Común than on any other cultivar. An inverse relationship of lesion size and total sporulation was observed. Común had significantly lower total sporulation than Híbrido and Holandés, which had the smallest average lesion sizes. These data show variation in pathogenicity of P. betacei isolates, under controlled conditions, and differential susceptibility of four distinct S. betaceum cultivars.

The focus of this research was to evaluate genotypes for cold-tolerant germination from wild switchgrass (Panicum virgatum L.) populations collected in the Northeast USA. Switchgrass nurseries were established in 2008 and 2009 with seed collected from native stands of switchgrass in the Northeast USA between 1991 and 2008. Switchgrass seed harvested from individual genotypes was evaluated for cold-tolerant germination in a series of laboratory experiments. Germination assays of seed of 13 switchgrass genotypes harvested in the fall of 2016 are the primary focus of this reported research. The selected genotypes were evaluated for cold-tolerant seed germination in three experiments, during the spring of 2017, fall of 2017 and spring of 2018, (with and without stratification) using a 10/15 °C regime with a 12 h photoperiod. Germination tests showed that several genotypes had significantly higher percentage germination as well as faster germination rates expressed as T50 (number of days required to reach 50% maximum germination) when compared to Cave-in-Rock, a moderately sensitive cold-tolerant commercial cultivar established in the original switchgrass nursery as a control. A final germination test was conducted to compare seed from the original population (no selection cycle 0), with one of the top performing cold-tolerant germination genotypes, and a commercial cultivar, 'Espresso', developed for low seed dormancy and low temperature germination. In this test, the selected genotype had significantly higher percentage germination in the stratified treatment and was not significantly different than Espresso in the non-stratified test. These data indicate successful selection for cold-tolerant germination in switchgrass genotypes from native germplasm collected in the Northeast USA., Competing Interests: The authors declare no conflicts of interest.