Morphological characteristics of flowers, duration of flowering, degree of self-pollination, and extent of berry and seed production in North American ginseng (Panax quinquefolius L.) were studied under controlled environmental conditions as well as under field conditions. A comparison was also made between plants of 3 and 4 years of age at two field locations. The duration of flowering was ≈4 weeks and was similar in plants of both age groups grown in the two environments; however, 4-year-old plants produced an average of 40% more flowers (≈100 per plant in total) compared to 3-year-old plants. Flowers were comprised of five greenish-colored petals, five stamens, and an inferior ovary consisting of predominantly two fused carpels and stigmatic lobes. Anthers dehisced in staggered succession within individual flowers, and flowering began with the outermost edge of the umbel and proceeded inwards. At any given time during the 4-week flowering period, ≈10% of the flowers in an umbel had recently opened and were producing pollen. Stigma receptivity was associated with separation of the stigmatic lobes; this occurred at some time after pollen release. Growth of pollen tubes through the style in naturally pollinated flowers was most evident when the stigmatic lobes had separated. The proportion of flowers that developed into mature berries (pollination success rate) was in the range of 41% to 68% for both 3-year-old and 4-year-old plants. However, when the inflorescence was bagged during the flowering period, berry formation was increased by 13% to 21% in 4-year-old plants, depending on location. A majority of the berries (92% to 99%) contained one or two seeds in an almost equal frequency, with the remaining berries containing three seeds. In 4-year-old plants, the frequency of two-seeded berries was increased by ≈13% by bagging the inflorescence. These observations indicate that P. quinquefolius is highly self-fertile and that several physiological and environmental factors can affect seed production.
Cayetana Schluter and Zamir K. Punja
Steve Rose and Zamir K. Punja
Eighteen cucumber (Cucumis sativus L.) cultivars (long English type) were screened for their susceptibility to fusarium root and stem rot caused by Fusarium oxysporum Schlechtend.: Fr. f.sp. radicis-cucumerinum D.J. Vakalounakis using seedlings at the third true-leaf stage. Roots were trimmed and dipped into a spore suspension (105 spores/mL) of the pathogen and the plants were re-potted. A disease severity index (DSI) was used to assess disease responses 4 or 8 weeks later based on plant mortality and the height of surviving plants compared to the noninoculated controls. `Sienna', `Amazing' and `Dominica' were most susceptible to infection and the resulting DSI values were significantly (P ≤ 0.05) higher compared to noninoculated control plants. The cultivars `Korinda', `Euphoria' and `Aviance' displayed significantly lower DSI values which were not significantly different from noninoculated control plants. The remaining 12 cultivars displayed DSI values which were intermediate between the above two classes of responses. The results from this study indicate there is the potential to identify and develop cultivars and breeding lines of greenhouse cucumbers with enhanced resistance to fusarium root and stem rot.
Ken K. Ng, Leslie MacDonald, and Zamir K. Punja
The efficacy of Tilletiopsis pallescens Gokhale, a naturally occurring ballistosporeforming yeast isolated from mildew-infected leaves, was evaluated as a biological control agent against rose powdery mildew [Sphaerotheca pannosa (Wallr.:Fr.) Lév. var. rosae Woronichin]. Two trials were conducted on potted rose (Rosa sp.) plants (1-year-old cv. Cardinal Pink) under commercial greenhouse-growing conditions during the summer (June to September) when mildew was most severe. Mildew-infected plants were subjected to one of four treatments: a T. pallescens spore suspension applied three times (3–4 d apart), distilled water (applied three times), one application of T. pallescens spore suspension, or one application of culture filtrate without spores. Two weeks after treatment began, mildew development was evaluated by enumerating conidial density on sampled leaflets. Sporulation was significantly reduced (by 97%–98%) on plants treated with three applications of T. pallescens spore suspension, compared to a 47%–57% reduction on plants treated with three applications of distilled water. There was no significant difference in conidial density between plants treated with one application of T. pallescens spore suspension and plants treated with one application of its culture filtrate, with a 78%–94% reduction in conidia, which was significantly higher than for the water treatment. The mode(s) of action of T. pallescens appears to be eradicant and associated with enzymes or metabolites produced in the culture filtrate. The results from this study demonstrate the potential for biological control of rose powdery mildew under commercial growing conditions in British Columbia.