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Rahmatallah Gheshm and Rebecca Nelson Brown

Lettuce (Lactuca sativa L.) is a popular crop for spring and fall high tunnels among direct-market vegetable producers. Common practices include the use of compost as a soil amendment, and reliance on cultivation for weed control. This study examined the impacts of using compost as a surface mulch to control weeds in spring and fall romaine lettuce, with data collected on soil temperature, weed suppression, and lettuce yields. Costs of all inputs, including labor, were tracked to assess economic feasibility of using mulch. Compost mulch was compared with bare ground with cultivation across four cultivars of romaine lettuce: Ridgeline, Coastal Star, Green Forest, and Shushan. In the fall experiment, mulching increased average soil temperature by 1 °C and canopy cover, leaf area index (LAI), and fresh and dry weights were significantly higher in mulched plots. Mulching decreased daily variation in soil temperature in the spring experiment but had no effect on average soil temperature. Canopy cover, LAI, and fresh and dry weights were not significantly affected by mulching in the spring experiment. Compost mulch affected all cultivars similarly in both experiments, with no significant interaction effects. Yields were greater and leaves were larger in the spring experiment than in the fall for all cultivars. Fresh weight yields in the spring experiment averaged 3.22 kg·m−2 and heads had a LAI of 7.9 as compared with 1.02 kg·m−2 and 1.6 for the fall experiment. Dry matter content (DMC) was significantly higher in the fall lettuce (113 g·kg−1) than in the spring lettuce (43 g·kg−1). Cultivar rank order was consistent across experiments, with ‘Ridgeline’ having the best performance and ‘Green Forest’ the worst. ‘Coastal Star’ and ‘Shoshone’ were intermediate and very similar to each other. Although the use of compost as a mulch increased yields of all cultivars in the fall experiment, only the top cultivar, Ridgeline, produced enough additional yield to offset the increased costs of the compost mulch used in this study. The use of a less-expensive compost or a higher retail price for romaine lettuce would have made the economics more favorable for the other cultivars.

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Mina Vescera and Rebecca Nelson Brown

Muskmelons (Cucumis melo L.) are routinely grown on black plastic mulch, as the associated increase in soil temperatures, more stable soil moisture, and decreased weed competition result in higher yields than in bare soil production. However, mulch does little to moderate air temperature, which can be below optimum for melon production under New England conditions. One option for increasing air temperature is to grow plants in unheated hoophouses, or high tunnels. Another option is to use low tunnels consisting of ventilated clear plastic rowcovers supported over wire hoops. This study compared low tunnels and high tunnels to open field production for muskmelon production in a peri-urban market farm system in Rhode Island. Five hybrid muskmelon cultivars were grown for 2 years to compare earliness, yield, and fruit quality among the three production systems. Both tunnel systems increased the rate at which growing degree-days (GDD) accumulated relative to open field production, and resulted in statistically significant differences in starting date of first harvest, with fruit in the high tunnel treatment ripening first. The high tunnel production system increased yields per hectare in both years relative to the other production systems due to increased planting density, but not due to increased yields per plant. Marketable yields per hectare from the high tunnel system significantly exceeded those from the open field for four out of the five cultivars in 2011, but for only one out of five cultivars in 2012. Marketable yields from the low tunnel system were ≈10% higher than the open field in 2011, and almost double the open field yields in 2012. Fruit from the low tunnels had the highest concentration of soluble solids in both years. The high tunnel production system did not increase yields sufficiently to offset the associated increase in costs of production, suggesting that muskmelon is not a good crop for high tunnel production in New England. In contrast, a yield increase of only 15% would be sufficient to offset the increased costs of employing the low tunnel production system. Low tunnels have the potential to greatly benefit muskmelon production in New England, particularly in years or locations where GDD accumulate slowly.

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Rebecca Nelson Brown and Peter D. Ascher

The methods of Wall and York (1957) were used to measure cotyledon position in two populations of three species interspecific Phaseolus hybrids and in the single species cultivars and accessions of P. coccineus, P. acutifolius, and P. vulgaris used as parents. Cotyledon position was represented by the length of the epicotyl as a percentage of the total length of the seedling's stem from the first root initial to the base of the primary node. Progeny of interspecific crosses between P. coccineus and P. vulgaris have been shown to inherit the cotyledon position of the cytoplasmic parent. The objectives of this study were to determine if three species hybrids also inherited the cotyledon position of the cytoplasmic parent, and to determine if P. acutifolius could be distinguished from P. vulgaris by its cotyledon position. Results indicated that the cotyledon positions of the three species hybrids did not differ significantly from the cotyledon positions of cultivars of the species used as the cytoplasmic parent for both P. vulguris cytoplasm and P. coccineus cytoplasm. Further, the cotyledon position of the P. acutifolius accessions did differ significantly from the cotyledon positions of both the P. vulgaris cultivars and the three species hybrid with P. vulgaris cytoplasm. These results suggest that cotyledon position may indeed be a species-specific trait for Phaseolus in Lamprecht's sense of the term.

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Rebecca Nelson Brown and James R. Myers

Marker-based selection for resistance to zucchini yellow mosaic virus in squash (Cucurbita spp.) would allow breeders to screen individual plants for resistance to multiple viruses. The C. moschata landrace Nigerian Local is widely used as a source of resistance in C. pepo breeding programs. We used RAPDs and bulk-segregant analysis to screen two BC1 populations for a marker linked to the dominant major gene for resistance from Nigerian Local. The initial cross was Waltham Butternut × Nigerian Local; the test populations were created from reciprocal backcrosses to Waltham Butternut. Both populations segregated 1:1 for resistance when hand-inoculated with ZYMV. RAPD primers were screened on a resistant bulk and a susceptible bulk from each population, and Waltham Butternut and Nigerian Local. Primers that gave bands linked to resistance were further screened using DNA from individual plants in each population. The potential markers will be tested on several populations derived from crosses between summer squash (C. pepo) and Nigerian Local to determine if they would be useful for selection in a C. pepo background.

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Harry S. Paris and Rebecca Nelson Brown

Pumpkin and squash (Cucurbita L. spp.) are important cucurbit crops and are grown in almost all arable regions of the world. The three economically important species, Cucurbita pepo L., Cucurbita moschata Duchesne, and Cucurbita maxima Duchesne are highly polymorphic in fruit characteristics, inspiring much research into their inheritance. A comprehensive list of genes for Cucurbita was last published more than a decade ago. This new gene list for pumpkin and squash includes descriptions of gene interactions and the genetic background of the parents that had been used for crossing to allow easy confirmation of previous work and provide a sound foundation for further investigation. This gene list includes 79 loci for phenotypic/morphological traits and 48 polymorphic allozyme loci. Linkage and mapping are discussed.

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Rebecca Nelson Brown and James R. Myers

A molecular and morphological marker map would improve our knowledge of Cucurbita genetics, and would facilitate efforts to breed improved summer and winter squash cultivars. Random amplified polymorphic DNA (RAPD) markers were used to construct a partial map of the Cucurbita genome. The mapping population was the BC1 progeny of the Cucurbita pepo L. yellow straightneck inbred A0449 and the tropical Cucurbita moschata Duchesne ex Lam. landrace `Nigerian Local'. A0449 was the recurrent parent. This cross was chosen because of the relatively greater economic importance of summer squash, traits of value to be introgressed from the C. moschata parent, and maximized genetic variation from the interspecific cross. The map contains 148 RAPD markers in 28 linkage groups. Loci controlling five morphological traits were placed on the map. The map covers 1,954 cM, which is estimated to be 75% of the Cucurbita genome. The qualitative traits placed on the map include the B gene for fruit which turn yellow before anthesis, the M gene for silver mottling of leaves, and a locus controlling the intensity of rind color on mature fruit. Quantitative trait loci (QTL) associated with fruit shape and the depth of the indentations between primary leaf veins were identified.

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Rebecca Nelson Brown and Josef H. Gorres

Highway rights-of-way are routinely planted with turfgrasses to prevent erosion, filter runoff, and improve aesthetics. However, the roadside is a harsh environment, and perennial grasses often die within the first year, leading to bare ground and annual weeds, which do not prevent erosion during the winter. To improve the survival of perennial vegetation on the roadside, it is necessary to identify the factors limiting vegetation growth and then to either identify plants that can tolerate those factors or identify ways to ameliorate the stresses while still maintaining safety. This study was designed to evaluate the effects of improved cultivars, salt tolerance, and organic matter amendments on perennial grass survival along two highways in Rhode Island. The amendments tested were processed biosolids and composted yard waste, each applied in a 50:50 mixture by volume with existing roadside soil; plain soil was included as a control. We tested 20 improved turfgrass cultivars and one seed mixture with common creeping red fescue (Festuca rubra L.) as the standard. Turfgrass species tested were perennial ryegrass (Lolium perenne L.), tall fescue (Festuca arundinacea Schreb.), red fescue, alkali grass [Puccinellia distans (Jacq.) Parl.], idaho bentgrass (Agrostis idahoensis Nash), tufted hairgrass [Deschampsia cespitosa (L.) P. Beauv.], and kentucky bluegrass (Poa pratensis L.). We found that soil amendment was more effective than either improved genetics or salt tolerance. Establishment, vertical growth, and persistence of vegetation cover were significantly improved by amendment with organic matter, particularly biosolids. In Summer 2009 (the second growing season), turf cover exceeded 50% in the biosolids plots but was below 20% in the plain soil plots with complete loss of cover in the plain soil plots at one location. Kentucky bluegrass, tall fescue, red fescue, and idaho bentgrass showed the best persistence at the species level, and there were no consistent differences among cultivars.

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Rahmatallah Gheshm and Rebecca Nelson Brown

Romaine lettuce (Lactuca sativa) is the most popular leafy vegetable in the United States. Organic and synthetic mulch materials are applied by farmers to reduce their weeding expenditures, manage soil temperatures, and increase the yield and quality of their crops. This study examined the impacts of using black polyethylene, compost, and shredded leaves as surface mulches in spring open field romaine lettuce by using data regarding the soil temperature, lettuce growth, and yield parameters. Mulch treatments were compared to determine effects on soil temperature, lettuce growth rates, leaf area index (LAI), yield, and plant size. Experiments were conducted in 2017 and 2019. Soil temperatures were slightly (but significantly) warmer in 2019, the plants grew more rapidly, and LAI, yield, and plant size were all significantly greater than they were in 2017. Mean soil temperatures were 18.0 and 18.9 °C in black polyethylene mulched plots, 17.7 and 18.5 °C in compost, 17.5 and 17.0 °C in bare ground, and 16.9 and 17.3 °C in shredded leaf plots in 2017 and 2019, respectively. Changes in canopy size presented a similar trend over the growing season for all treatments; shredded leaf and bare ground treatments on all measuring dates had the smallest canopy size, and compost and black polyethylene mulches had the largest canopy sizes. Black polyethylene and compost mulches had the highest LAI and yields in both years. In 2017, the bare ground treatment was similar to black polyethylene and compost mulch treatments for both parameters, and all three treatments were significantly greater than the shredded leaf mulch treatment. In 2019, the bare ground treatment was similar to the shredded leaf mulch treatment and significantly lower than the black polyethylene and compost mulch treatments. In 2017, black polyethylene and compost mulches had LAI of 7.67 and 7.37 and yields of 6.38 and 6.68 kg·m−2, respectively. Bare ground had an LAI of 7.16 and yielded 5.94 kg·m−2. Shredded leaf mulch plots had the lowest LAI (5.94) and yield (4.96 kg·m−2). In 2019, the bare ground treatment had an LAI of 7.5 and yielded 7.6 kg·m−2. Black polyethylene and compost mulches increased LAI by 1.7. Yield increased by 2.8 kg·m−2 with black polyethylene mulch and by 2.4 kg·m−2 with compost mulch. Shredded leaf mulch produced LAI and yield similar to but slightly lower than bare ground. Dry weight, plant height, and head diameter in bare ground and shredded leaf mulch treatments were significantly smaller than in black polyethylene and compost mulch treatments. The cultivar rank order was consistent across treatments in both years; ‘Ridgeline’ grew significantly faster than ‘Coastal Star’, and plants were significantly larger at harvest. Black polyethylene suppresses weeds and increases soil temperatures, thereby enhancing yields of spring-to-summer romaine lettuce under southern New England conditions. Compost mulch has similar effects on yields. Shredded leaf mulch is effective at suppressing weeds but decreases soil temperatures and yields.

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Rebecca Nelson Brown, Cynthia Percivalle, Sophia Narkiewicz, and Samantha DeCuollo

Erosion is a significant problem on highway embankments in Rhode Island. At present, a mixture of red fescue (Festuca rubra L.), perennial ryegrass (Lolium perenne L.), and kentucky bluegrass (Poa pratensis L.) is planted to stabilize the soil. However, only the red fescue survives long term on slopes. Red fescue is shallow-rooted, leading to sod sloughing after heavy rains. The objective of this study was to compare the rooting depth, plant height, and adaptation to roadside conditions of 16 native grasses and five amenity grasses with red fescue to identify species that could be used to reduce sod sloughing. Research was conducted from May 2006 through Aug. 2009 in the greenhouse at the University of Rhode Island in Kingston and on the shoulder of state Route 4 in North Kingstown, RI. The cool-season grasses smooth brome (Bromus inermis Leyss. ssp. inermis), Pumpelly's brome [Bromus inermis Leyss. ssp. pumpellianus (Scribn.) Wagnon], Canadian wildrye (Elymus canadensis L.), Virginia wildrye (Elymus virginicus L.), silky wildrye (Elymus villosus Muhl. ex Wild.), eastern bottlebrush (Elymus hystrix L.), perennial ryegrass, and tall fescue (Festuca arundinacea L.) and the warm-season grasses little bluestem [Schizachyrium scoparium (Michx.) Nash] and purple lovegrass [Eragrostis spectabilis (Pursh.) Steud.] were similar in height to red fescue while rooting significantly more deeply. Of these 10 species, little bluestem, purple lovegrass, and tall fescue showed the best survival on the roadside.

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Jeffrey R. Pieper, Rebecca Nelson Brown, and José A. Amador

Most vegetable farms in southern New England market directly to consumers and are characterized by high crop diversity and intensive cultivation. Growers rely on tillage to prepare fields for planting and control weeds, but are concerned about the negative effects of tillage on soil health. This study evaluated three tillage reduction strategies in a market garden system producing tomatoes, melons, cucumbers, cabbage, carrots, and lettuce. Treatments of strip tillage into a killed cereal rye (Secale cereale) cover crop mulch, perennial white clover (Trifolium repens), and ryegrass (Lolium perenne) living mulch between planting rows, and annual crimson clover (Trifolium incarnatum) living mulch interseeded between vegetable rows were established in 2010 and compared over 3 years to a control system using tillage to maintain bare ground between rows. Treatments were evaluated for effects on vegetable yield and soil biological, chemical, and physical properties. The strip tillage treatment was the most effective at promoting soil health, resulting in significant increases in soil aggregate stability, potentially mineralizable nitrogen, active soil carbon, and microbial activity relative to the control, and significant decrease in loss of soil organic matter. However, it was not effective for production of vegetables, with the strip-tillage plots having the lowest yields throughout the study. The perennial living mulch treatment produced yields of carrots, melons, and cucumbers similar to the control yields, but reduced yields of tomatoes, cabbage, and lettuce. Microbial respiration was significantly higher than in the control, and nitrate levels, and loss of soil organic matter were significantly lower. The annual living mulch treatment produced yields similar to the control for all crops, and soil health was similar to the control for all variables except soil nitrate, which was significantly higher than the control. Perennial living mulch shows the most promise for improving soil health while maintaining yields in some vegetable crops, but challenges remain in preventing competition between vegetables and living mulches.