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Heather H. Friend and Dennis R. Decoteau

Alterations in spectral distribution as affected by selective light transmission of row cover materials were evaluated for effects on early watermelon (Citrullus lanatus cv. Sugar Baby) growth and development. Selected commercially available row covers were analyzed for light transmission properties. Results suggest that row cover materials function as selective light filters and influence parameters of light that can affect plant morphogenesis. Clear polyethylene row covers caused little variation in transmitted PAR (photosynthetically active radiation) and photomorphogenic light (FR/R and blue light). White polyethylene row covers decreased the transmitted PAR and blue light but had no effect on the FR/R ratio. Watermelon plants grown under a white polyethylene row cover with a greater FR/R ratio of light were taller (longer stems) and had longer petioles than plants grown under a clear polyethylene row cover with a smaller transmitted FR/R ratio.

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Dennis R. Decoteau and Heather H. Friend

The influence of end-of-day (EOD) supplemental light-priming on pepper (Capsicum annuum cv. Keystone Resistant Giant No. 3) transplants was investigated for possible residual growth effects on subsequent plant growth and fruit production. Greenhouse grown pepper transplants were fluorescent light-primed for one hour prior to dusk for three weeks in 1988 and four weeks in 1989 and then transplanted to the field. EOD fluorescent light-priming of pepper plants reduced the height, leaf area, dry weight, fruit number, and fruit weight as compared to non-treated plants prior to first harvest. EOD fluorescent light-priming of pepper transplants had little effect on early and total fruit production. These results suggest that EOD fluorescent light-priming of transplants that affect early pepper growth in the field have little residual influence on subsequent fruit production.

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Heather H. Friend and Dennis R. Decoteau

The effect of planting density on yield and pod distribution of cayenne pepper (Capsicun annuum var. annuum L. cv. Carolina Cayenne) was investigated in a two year study. In 1988, planting density was adjusted by altering the in-row spacing of single row beds, while in 1989 planting density was adjusted by altering both in-row spacing and number of rows per bed. In-row spacings evaluated in 1988 were 60, 45, 30, and 15 cm, while in-row spacings of 60, 30, and 15 cm in single and double rows were evaluated in 1989. In 1988, pepper plants grown in the highest density (15 cm in-row spacing) produced less fruit per plant, but more fruit per hectare than those grown in lower densities. In 1989, greatest yields per hectare were recorded with either 15 cm in-row spacings with single rows per bed or 30 cm in-row spacings with double rows per bed, In general, greater percentages of fruits were located in the upper part of the plant canopy when planted in higher plant densities.

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Dennis R. Decoteau and Heather H. Friend

Phytochrome-regulated growth of watermelon [Citrulls lanatus (Thunb.) Matsum & Naki cv. Sugar Baby] was investigated by treating plants with brief exposures of red (R) or far-red (FR) light at the end of the daily photoperiod. Light treatments were initiated when the plants were 2 weeks old (two true-leaf stage). After 4 days of treatment, petiole lengths of leaf 1 (first leaf above the cotyledon) and leaf 2 (second leaf above the cotyledon) were longer, and the angle formed between these two petioles was more acute in plants treated with end-of-day (EOD) FR than in plants treated with EOD R light or non-EOD-treated plants (control). After 7 days of treatment, internodes 2 and 3 and petioles from leaves 1, 2, and 3 were longer from plants treated for 7 days with EOD FR light than from plants treated with EOD R light or from controls. The EOD FR light promotion of internode, petiole angle, and petiole elongation was reversible by immediately following the FR with R, implicating the involvement of phytochrome in the regulation of these growth processes of watermelon. After 21 days of treatment, most of the internodes (six of eight) from the EOD FR-treated plants were longer than the corresponding internodes from the EOD R-treated plants. Plants that were treated with EOD light for 21 days and then grown for an additional 14 days without EOD light treatments exhibited no residual EOD light effect on internode elongation (as compared to plants not exposed to EOD light). Residual EOD FR light treatment effects on elongation of petioles 1, 2, 3, and 4 were suggested for plants treated with EOD light for 21 days and then grown for 14 days without EOD treatments.

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Heather H. Friend and Dennis R. Decoteau

The effect of planting density on yield and pod distribution of cayenne pepper (Capsicun annuum var. annuum L. cv. Carolina Cayenne) was investigated in a two year study. In 1988, planting density was adjusted by altering the in-row spacing of single row beds, while in 1989 planting density was adjusted by altering both in-row spacing and number of rows per bed. In-row spacings evaluated in 1988 were 60, 45, 30, and 15 cm, while in-row spacings of 60, 30, and 15 cm in single and double rows were evaluated in 1989. In 1988, pepper plants grown in the highest density (15 cm in-row spacing) produced less fruit per plant, but more fruit per hectare than those grown in lower densities. In 1989, greatest yields per hectare were recorded with either 15 cm in-row spacings with single rows per bed or 30 cm in-row spacings with double rows per bed, In general, greater percentages of fruits were located in the upper part of the plant canopy when planted in higher plant densities.

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Heather. H. Friend, Arne Sæbø, and Dennis R. Decoteau

Previous research has demonstrated that watermelon plants are sensitive to changes in light quality, as suggested by an individual treatment of plants with 15-min of end-of-day (EOD) red (R)and far-red (FR) light. FR-induced growth responses (i.e., petiole elongation, internode elongation, reduced petiole angles) were reversed by immediately following the FR light treatment with R light implicating phytochrome as the light quality perception mechanism. The objective of the present experiment was to determine the influence of individual and multiple FR light treatments (each treatment of 15-min duration) during the light and dark phase of the photoperiod on photomorphogenic growth responses of young watermelon plants. Light regulated growth responses of watermelon were influenced by the timing and the number of light quality exposures during the light or dark phase of the photoperiod. Individual FR treatments during the light phase except for the EOD exposure did not affect plant growth responses. In contrast, individual FR treatments at selected intervals during the dark period affected plant development. The most effective individual FR treatment to induce growth responses was at the beginning of the dark period, with decreasing responses as the FR treatment was delayed into the dark period. Multiple exposures of FR during the dark slightly increased growth responses as compared to a single EOD FR treatment.

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Dennis R. Decoteau, Heather H. Friend, Dale E. Linvill, and George Upton

We have developed and field tested a plastic mulch system that changes color with season. The system uses a photodegradable polyethylene mulch placed on top of a degradable or nondegradable polyethylene mulch of a different color. As the top polyethylene mulch degrades with increasing exposure to sunlight, the color of the bottom polyethylene mulch is exposed. We have successfully evaluated the effects of a black photodegradable mulch placed on top of a white nondegradable mulch on mulch color transition, soil temperatures under the mulch, and the production of spring planted tomatoes. The mulch color system affected soil temperatures and average tomato fruit size, but had no effect on number of fruit produced. We have also produced and are field testing a coextruded polyethylene mulch with the desired black and white photodegradable colored layers.