Acorn squash (Cucurbita pepo L.) is one of the three major classes of squash consumed in North America. Breeding improvements over the past 30 years have focused on more compact cultivars, earlier maturity, darker rind color, and powdery mildew tolerance (PMT). Our observations from sampling acorn squash from local supermarkets at different times during the year show that eating quality is highly variable, and most often, not acceptable. Our taste tests indicate that for acceptable eating, quality acorn squash should have °Brix of 10 or higher, flesh %DW above 16, and a smooth, nonfibrous texture. Most commercial cultivars fail to meet the above minimum criteria for quality. Proper harvest time is a major determinant of squash eating quality. To obtain adequate °Brix levels, squash should not be harvested until at least 50 days after pollination (DAP). If squash are harvested between 25 to 40 DAP and then stored for two or more weeks, °Brix levels may increase to acceptable levels, but some mesocarp reserves will be remobilized to developing seeds, reducing mesocarp %DW and lowering eating quality. A major goal of the squash breeding efforts at the University of New Hampshire has been to increase mesocarp %DW for obtaining more consistent eating quality. We have evaluated several experimental PMT hybrids during the past 5 years, and in some of these, flesh DW has averaged 17% or higher, and eating quality has been rated consistently very good. The adoption of better quality acorn cultivars together with implementing proper harvest times and storage conditions could appreciably increase per capita consumption.
J. Brent Loy
Premature harvest of acorn squash is a widespread problem because fruits reach maximum size and optimum color within 20 days after pollination (DAP), well before peak dry matter and sugar content occur. The present study was conducted to determine the relationship between harvest date and physiological factors affecting eating quality in Cucurbita pepo L. squash. In the summer of 2005, C. pepo squash cultivars were evaluated at three harvest dates, 25, 35, and 45 days after pollination (DAP), with or without a 10-day storage period at 21 °C. Four F1 hybrid cultivars carrying powdery mildew tolerance (PMT) were evaluated: a semi-bush, commercial acorn cultivar (`Tip Top'), a high quality experimental acorn, bush hybrid (NH1634), and two sweet dumpling-type, semi-bush hybrids (NH1635 and 1636). Data were collected on mesocarp DW, oBrix (soluble solids), and partitioning of biomass between mesocarp tissue and developing embryos during storage. Peak DWs of 20% to 21% occurred at 25 DAP in NH1634, 1635 and 1636, and at 35 DAP in Tip Top (19.5 %). At 25 DAP, Brix was low (means of 5.9 to 7.2) across all cultivars. With harvest at 25 DAP plus 10 days storage, oBrix was low in Tip Top (7.1), but was higher than 10 in NH1634 and NH1636. Brix reached near maximum (13 to 15) at 45 DAP in NH1634, 1635 and 1636, and at 55 DAP in Tip Top (12). Embryos were small (DW = 8 to 19 mg) at 25 DAP and grew fairly linearly to a maximum at 55 DAP. Mean embryo DW at 55 DAP was 87.5 mg for Tip Top, 76.9 mg for NH1636, 57.1 mg for NH1634, and 28.5 mg for NH1635. The proportion of total fruit biomass expressed as energy equivalents (kJoules) allocated to embryos in mature fruit (45 DAP + 10 days storage) was 11.8% in NH1635, 18.7% in NH1634, 27.4% in Tip Top, and 30.2% in NH1636. Reallocation of assimilates from mesocarp tissue to developing embryos was a major contributing factor, along with respiration, to a reduction in mesocarp dry matter during storage.
Amy Ouellette and J. Brent Loy
A field study was conducted to compare the effect of different planting densities and polyethylene mulch treatments on growth and yield of `Mountain Fresh' trellised tomato grown on raised beds on 1.8-m centers. The experiment design was a split plot with four replications and four mulch treatments as main effects: 1) standard black mulch (B), 2) Sonoco red mulch (R), 3) black mulch with interrow (between beds) reflective white on black mulch (B/W), and 4) red mulch with inter-row R/W. Subtreatments were three within-row spacings: 1) 0.60 m (8966 plants/ha); 2) 0.45 m (11955 plants/ha; standard spacing), and 3) 0.30 m (17932 plants/ha). Yield was determined from eight-plant plots and adjacent plants were harvested at regular intervals to determine plant biomass accumulation and partitioning of biomass among roots, stems, leaves, and reproductive organs. There was a linear increase in yield among mulch treatments with increasing plant density. The B/W mulch treatment increased midseason and total yields ≈20% over that of the other mulch treatments. Fruit yield of plants with the B/W mulch treatment at the 0.3-m spacing was 54% higher (151 MT/ha) than that of plants grown on black mulch with the standard plant spacing of 0.45 m (97.9 MT/ha). There was a linear decrease in fruit size with increasing plant density; however, plants grown at the 0.30-m spacing on the B/W mulched plots exhibited only a 2.7% decrease in fruit size as compared to plants grown at the standard 0.45-m spacing on black mulch.
Qiubin Xiao and J. Brent Loy
This study was undertaken to determine the inheritance of a glabrous trait discovered in yellow straightneck summer squash (Cucurbita pepo L.) in 1992 and to compare trichome distribution and anatomy and morphologic features that relate to productivity in glabrous and nonglabrous genotypes. Inheritance data from 1994, 2003, and 2004 confirm that the glabrous trait is inherited as a single gene recessive, designated gl-2, but that in some segregating F2 populations with a zucchini or caserta (C. pepo ssp. pepo) background, there is a deficiency of glabrous segregants. Nonglabrous (NG) plants bore numerous trichomes on stems, petioles, leaf blades, and fruit. Trichomes were simple (unbranched), and most were either conical and unicellular or small filiform and multicellular (two to five cells). However, some larger multicellular trichomes with compound feet were found on major leaf blade veins and along vein tracts of petioles. Large, multicellular trichomes with compound feet were only occasionally present on leaf blades and petioles of glabrous (G) plants, and other trichome types were much reduced. This reduction gives fruit and foliage a smooth, waxy feel and largely eliminates trichome damage to fruit and skin irritation to workers during harvesting. Leaf number, staminate to pistillate flower ratios, and fruit size were not significantly different between glabrous (gl-2/gl-2) and nonglabrous (Gl-2/gl-2) backcross (BC) genotypes. In one of two BC populations, pistillate flowering was 2 d earlier in NG as compared with G plants. The glabrous gene reduced the size of leaf blades in two BC populations; however, differences in total leaf areas were not statistically significant at P = 0.05. A comparison of leaf numbers and size among G and NG parental plants and reciprocal F1 hybrids derived from three separate crosses did not reveal a consistent effect of the gl-2 gene on plant morphology. Earliness and productivity of the best glabrous hybrids were similar to that of popular commercial cultivars.
Jake Uretsky and J. Brent Loy
Interspecific hybrids can be produced from certain cross combinations of Cucurbita maxima x C. moschata. These hybrids have been used extensively as rootstocks for melon and watermelon grafting, but only occasionally for fresh market use. The objective of this study was to assess the potential of interspecific hybrids for use in pie processing in terms of morphological traits related to productivity. We used a bush-processing inbred line of C. maxima, NH65, as the female parent and two vining-processing cultivars of C. moschata, Long Island Cheese (LIC) and Dickinson Field (DF) as pollen parents to produce two interspecific hybrids with large orange fruit, potentially suitable for processing. A greenhouse study was conducted to compare internode lengths, main stem diameters, flowering patterns, and leaf area at first appearance of female flowers in NH65, LIC, DF, and two interspecific hybrids, NH65xLIC and NH65xDF. Plants were grown in 8.7 L nursery pots, watered and fertigated with drip tubing, and trellised to a single main stem. In LIC and DF, internode lengths increased rapidly beyond the fourth node before reaching a maximum by node 12. Internodes in NH65 did not exceed 3 cm until node 15, and average lengths never exceeded 4 cm. In interspecific hybrids, internode lengths mimicked bush plants for 6 or 7 internodes, remaining below 3 cm, but then increased rapidly to lengths approaching that of the vining cultivars after internode 10. Staminate flowers were more abundant than pistillate flowers in NH65, LIC and DF; whereas the interspecies hybrids produced primarily pistillate flowers. In NH65xLIC, the first pistillate flowers appeared on nodes 9–11, on average 38.3 days after transplanting (DAT), and in NH65xDF, on nodes 9–17, 42.3 DAT. First pistillate flowers in NH65 occurred on nodes 9–11, 34.3 DAT, compared with nodes 9–13, 39.3 DAT and nodes 17–21, 50.0 DAT, respectively, for LIC and DF. A field study was conducted for comparing flowering patterns and growth habits in NH65xLIC, NH65xDF, DF, LIC, NH65, and ‘Golden Delicious’ (GD), a popular C. maxima processing winter squash. Stem length was short and petioles highly elongated in the two interspecific hybrids until about 34 DAT, such that plants exhibited a uniform, compact phenotype similar to NH65. Subsequently, stems elongated rapidly, with lengths approaching and occasional exceeding those in vine cultivars. In the two vining C. moschata cultivars, LIC and DF, 4–6 laterals developed near the base of plants, usually consisting of 12–30 nodes. NH65xLIC produced mostly short laterals (4–15 nodes) interspersed along much of the main stem, whereas NH65xDF produced numerous lateral branches, mostly ranging from 11 to 30 nodes long, between the base and about the halfway point along the main stem. Mature leaves were about twice as large in the two interspecific hybrids as in DF and GD; this together with differences in early growth habit and branching patterns contributed to a much faster leaf canopy cover in the interspecific hybrids in comparison with the vining cultigens.
Rosanna Freyre and J. Brent Loy
Five tomatillo (Physalis ixocarpa Brot. ex Hornem) cultivars available from commercial seed companies (`De Milpa', `Puebla Verde', `Purple Tomatillo', `Tomatillo' and `Toma Verde') and four Physalis L. accessions (PI 197691, PI 270459, PI 291560, and PI 309812) were grown in 1997 and 1998 at Kingman Research Farm, Durham, N.H. Three manual harvests per plot were performed each year, recording data of total fruit weight, number of fruit and average fruit weight for each genotype. There were statistically significant differences between tomatillo genotypes for all three traits. Statistically significant differences between the 2 years were found for fruit number and average fruit weight per genotype. Over both years, total fruit weight varied from 29.7 to 63.7 t·ha-1 (13.3 to 28.4 ton/acre). Fruit numbers per plant varied from 83 to 330, and average fruit weight varied from 18.0 to 38.3 g (0.6 to 1.3 oz). PI 197691 and PI 270459 performed better than some of the commercial cultivars indicating their potential to be used as germplasm for breeding. A basket-weave trellising system which kept plants upright was tested. This made harvest easier and potentially can be used for tomatillo culture.
Mark G. Hutton and J. Brent Loy
Robert L. Chretien and J. Brent Loy
A field study was conducted to compare seed yield and fruit biomass partitioning among 11 F1 hybrid snackseed (hull-less seeded) pumpkins. Experimental plots were seeded on 3 June 1999, using a randomized complete-block design with four replications and 20 plants per plot. Rows were spaced 1.8 m apart; within-row spacing was 0.3 m. The plots were divided in half with 10 plants for fruit and seed yield determinations and 10 plants for fruit biomass partitioning studies. Seed yields among hybrids ranged from 818 kg·ha-1 for NH1003 to 1575 kg·ha-1 for NH1041. The three highest-yielding hybrids (NH1030, NH1040, and NH1041) were derived from sister lines crossed to a common parent and were characterized by small fruit size (0.8 to 1.4 kg) and high seed biomass per kilogram of fruit fresh weight. The next highest-yielding group of hybrids (NH1024, NH1043, NH1044, and NH1045) also had small fruit, and two pairs of hybrids, NH1024/NH1043 and NH1044/NH1045, each shared a common parent. The four lowest-yielding hybrids (NH1003, NH1025, NH1027, and NH1029) were characterized by larger fruit (2 to 3 kg) and low seed yield per kilogram fruit fresh weight, but had larger seeds (average between 175 to 183 mg) than the other hybrids (130 to 165 mg). Peak percent dry matter of mesocarp tissue at 35 days postanthesis (PA) was lowest in large-fruited hybrids and highest in the highest-yielding hybrids. In most hybrids, percent dry matter decreased between 35 days PA and fruit maturity (65 days PA), indicating a shortage of photosythates needed for maintaining mesocarp biomass and maximizing seed fill. The highest-yielding varieties partitioned a greater portion of fruit biomass into seeds rather than flesh. Seed yield per plot was highly correlated with seed yield per kilogram of fruit fresh weight.
R. Bruce Carle and J. Brent Loy
The expression and inheritance of the fused vein trait in Cucurbita pepo were investigated. The fused vein inbred, NH2405, was crossed to normal lines, NH614, and NHBP10. Reciprocal F1, F2, F3 and BC populations were generated and examined for leaf type segregation in field and greenhouse environments. Although the fused vein phenotype is stable in NH2405, it exhibited a continuum of expression in segregating populations. The onset of vein fusion ranged from the fourth to the tenth leaf stage and degree of fusion varied from slight (1-5 cm) to extreme (10-20 cm). Inheritance ratios varied with population, conditions of production, and direction of cross. Most segregating populations fit either a single or double recessive gene model, however, a quarter of the populations showed no or low fused vein recovery. A feasible explanation for the distorted inheritance is that the fused vein trait is a gametophytic subvital, governed by a single recessive gene, fv. Although less likely, a double recessive, subvital model cannot be ruled out.
R. Bruce Carle and J. Brent Loy
Two experiments were conducted to test and delineate gametophytic subvitality of the fused vein trait in Cucurbita pepo. Gametophytic subvitality was verified by comparing pollen tube growth for fused vein and normal pollen in situ. Microscopic examination of partitioned, co-pollinated distillate flowers revealed inferior fused vein gametophyte performance. Normal pollen tubes grew faster and were significantly more abundant in the lower portion of the style. The consequences of gametophytic subvitality on seed yield and inheritance were shown by manipulating the severity of pollen competition. Fused vein, normal and F1 lines were pollinated with fused vein, normal, F and a 50:50 pollen mix at three different pollen loads. Fused vein pollen generated significantly fewer seed per fruit in all female genotypes. As a constituent in F, or mixed pollen, it produced significant seed yield reductions at the low pollen load. In F1 and testcross populations, a reduction in pollen load and therefore pollen competition significantly increased the number of fused vein individuals in segregating populations.