The Pythium flora of 2132 soil samples from all sections of the United States was determined using an apple trapping method and two selective media. Isolates of the P. irregulare – P. debaryanum complex were obtained from 90% of the samples, and made up 55% of the 10 566 isolates examined. Isolates referable to the P. dissotocum – P. perniciosum complex, P. spinosum, P. splendens, P. ultimum, P. vexans, and heterothallic forms including P. sylvaticum, P. heterothallicum, and P. intermedium were obtained from 5 to 15% of the samples. Pythium afertile, P. aphanidermatum, P. dissotocum – P. perniciosum, P. irregulare – P. debaryanum, P. spinosum, P. torulosum, P. ultimum, and the heterothallic species were found in soil samples from 60% or more of the sections of the country sampled. The following species were isolated infrequently: P. acanthicum – P. oligandrum complex, P. catenulatum, P. helicoides – P. oedochilum complex, P. mamillatum, P. middletoni, P. myriotylum, P. paroecandrum, P. periplocum, P. prolatum, P. pulchrum, P. rostratum, P. vexans, Phytophthora cinnamomi, and P. parasitica.

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Three Botryosphaeria spp. were grown on autoclaved apple and peach stems in cotton-plugged tubes with constant moisture at 6, 12, 18, 24, and 30°C to determine the effect of temperature on sporulation. Number of conidia per pycnidium was determined weekly from 4 to 10 weeks after inoculation. The experiment was repeated three times. Maximum sporulation occurred at 24°C with B. dothidea and at 18 and 24°C with B. obtusa. Spore production of both fungi showed a quadratic curvilinear response to temperature. Pycnidia were erumpent, typical of their habit in nature. Maximum sporulation of B. rhodina occurred at 12, 24, and 30°C instead of at a distinctive peak. Of the three fungi, B. rhodina produced the greatest number of conidia per pycnidium at all temperatures. Mycelia and pycnidia of B. rhodina grew on top of the bark, which is atypical of their habit in nature. For spore production by B. dothidea, there was a significant interaction between temperature and time. Maximum sporulation over the 10-week period occurred in week 4 and/or 6 for B. dothidea at 12, 18, and 24°C, with a linear response at 12 and 24°C (P ≤0.05). Conidial maturation of B. obtusa and B. rhodina had a quadratic curvilinear response due to temperature, with a maximum maturation at 12, 18, and 24°C with B. obtusa and at 24°C with B. rhodina. Spore maturation would affect longevity of conidial viability. Maximum spore production over time and percent pigmented spores over time by B. obtusa, and spore maturation over time by B. rhodina occurred in weeks 8, 9, and 10 with a significant linear response (P ≤ 0.05). All three Botryosphaeria spp. produced conidia over the 6 to 30°C range and over the 7-week period (weeks 4 to 10), with maximum sporulation or spore maturation at 18 to 24°C.

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