Once-over Harvest Research Articles

Genotype X Environment Interaction for Yield of Pickling Cucumber in 24 U.S. Environments

Abstract Reliable yield performance is important in cucumber because seed companies prefer to market cultivars adapted to multiple rather than single regions of the U.S. Also, growers benefit by using a cultivar that performs well in many environments. Future performance of cultivars is also important. The objectives of the study were to (i) evaluate the yield of cucumber genotypes over successive years and in different locations, and (ii) identify cucumber genotypes with high stability for yield. A diverse set of 22 pickling genotypes was evaluated over 3 years (1986, 1987 and 1988) and in 7 locations across the United States. Yield traits were evaluated using once-over harvest and counting the number of fruit that were marketable, culled or oversize. Total yield, marketable yield (total minus culled fruit), early yield (number of oversize fruit), percent culls and fruit per plant were calculated. Data were analyzed with SASGxE and RGxE programs using SAS and R programming languages, respectively. There were strong effects of environment(E) as well as genotype(G) xE interaction for all traits. Genotypes ‘Regal F1’, ‘Calypso F1’, ‘Carolina F1’, ‘Gy 3’, ‘Gy 14’ and ‘Fremont F1’ had high marketable yield and medium to high stability for all traits. There was an advantage of hybrids over inbreds for trait performance. Hybrids fell into a single cluster with large prediction intervals. Based on the stability statistics and divisive clusters, it appears possible to breed stable cucumber genotypes with high yield. The genotype with highest performance for marketable yield, greatest stability for yield, lowest 1-R2 ratio value (diverse and representative) were ‘Marbel F1’ and Gy 14.

Optimizing Sweetpotato Seed Root Density and Size for Slip Production

There is a research gap with respect to documenting the effects of sweetpotato (Ipomoea batatas) seed root density and size on transplant yield and quality. Field studies were conducted in 2012 and 2014 to determine the effect of sweetpotato seed root (canner size) density [12, 24, 37, 49, 61, 73, and 85 bushels [bu (50 lb)] per 1000 ft2] on ‘Covington’ and ‘Evangeline’ slip production in propagation beds. Another field study was conducted in 2012 and 2013; treatments included canner, no. 1, and jumbo-size ‘Covington’ roots at 49 bu/1000 ft2, to determine the effect of seed root size on slip production. As seed root density increased in the propagation bed, transplant production increased with no change in slip quality as measured by node counts and slip length except for stem diameter. In 2012, the best marketable slip yield was obtained at root densities of 73 and 85 bu/1000 ft2. In 2014, marketable slip production of ‘Evangeline’ increased as seed root density increased at a greater rate than ‘Covington’. In 2014, the best seed root density for marketable slip production was 49 to 85 bu/1000 ft2 for ‘Covington’ and 85 bu/1000 ft2 for ‘Evangeline’. In 2012, potential slip revenues increased with an increase in seed root density up to 73 bu/1000 ft2. In 2014, revenue trend was similar for ‘Covington’ as 2012; however, for ‘Evangeline’, revenue was greatest at 85 bu/1000 ft2. Seed root size had no effect on marketable slip production when using a once-over harvest system. Results suggest growers would use a seed root density from 49 to 85 bu/1000 ft2 depending on variety, and any size roots for production of optimum marketable slips. Selection of optimum seed root density also depends on grower needs; e.g., high seed root density strategy will have a higher risk due to the upfront, higher seed costs, but potentially have higher profits at harvest time. Lower seed root density strategy would be a lower initial risk with a lower seed cost, but also potentially have lower net revenues.

Evaluating pickling cucumber plant populations to maximize yield for once-over mechanical harvest in the southeastern United States

Evaluating pickling cucumber plant populations to maximize yield for once-over mechanical harvest in the southeastern United States

Applications of Nutrient-Controlling and Growth-Regulating Chemicals to Enhance Yield of Once-Over Harvest Red Pepper (Capsicum annuun L.)

The cultivation of once-over harvest pepper cultivars might be very valuable to Korean farmers who still depend on traditional hand-harvesting method. Thus, we conducted this experiment to obtain important information for enhancing the productivity of once-over harvest red pepper fruits by supplying several nutrient-controlling and growth-regulating chemicals, such as KH 2 PO 4 , SiO 2 , and 2-chloroethylphosphonic acid (ethephon). Adequate fertilization was provided in each treatment plots. In this study, two once-over harvest pepper cultivars, Saengryeg No. 211 and 213 (SR 211 and SR 213), and one regular piecemeal harvest pepper cultivar, Kangryegdaetong (KRDT), were cultivated to evaluate the productivity of pepper fruit as affected by above chemicals. The distribution of macro- and micro-nutrients in pepper fruits among the cultivars were different in term of N, B, Cu, and Fe concentrations. In particular, the concentration of B in SR 213 was about 2 times higher than that in SR 211 and KRDT. However, overall red pepper productivity of SR 211 was markedly higher (2.91~3.38 Mg ha -1 ) than that (1.68~2.37 Mg ha -1 ) of SR 213. Also, the productivity of matured red pepper was significantly influenced by the treatments of KH 2 PO 4 , SiO 2 , and ethephon. The yield indices for matured red pepper fruits were the highest with the treatment of KH 2 PO 4 or SiO 2 with ethephon, which were 113~116% for SR 211 and 147~150% for SR 213. Thus, the applications of KH 2 PO 4 or SiO 2 with ethephon would be suggested to enhance the productivity of matured red pepper fruit.

A Proposed Alternative Production Regime for Cherry and Grape Tomato Using Compact Plants and Once-over Harvest

This report presents preliminary data and arguments supporting the investigation and possible adoption of a low-cost method of cherry and grape tomato (Solanum lycopersicum) production. Cherry and grape tomato crops are currently grown using indeterminate or relatively large determinate plants requiring trellising and significant hand labor at harvest. In contrast, processing tomato crops are usually determinate cultivars raised without supporting systems, and they are harvested mechanically. In Summer 2009, a Mississippi trial of home garden tomato cultivars included a compact, mounding yellow-fruited cherry tomato that produced more than 2 kg of fruit per plant in the first harvest. The architecture of the plant, high yield potential, and concentrated set indicate that there is potential to grow commercial cherry and grape tomato crops in much the same way commercial processing tomatoes are grown: unsupported on bare or mulched beds, with once-over harvest. Such a system could reduce the monetary and labor costs of production of cherry and grape tomatoes. Seed companies, tomato growers, and supporting agencies should work together to further investigate the potential of this system of cherry and grape tomato production.

"Birdsnest" melons from Iran: Germplasm for concentrated yield in time and position

Melons (Cucumis melo) are an important vegetable crop. Melons are grown mostly for their sweet mature fruits, which are eaten fresh, but elongate-fruited forms are grown for their rather bland, juicy, immature fruits, which are eaten fresh, cooked, or pickled like cucumbers. Fruit set of melons is diffuse over time and space, resulting in the need for multiple harvesting of the crop. The phenotype, which originated in Iran, offers a germplasm source of concentrated fruit set and the possibility of reducing the number of harvests or even allowing a profitable once-over harvest. Herein are summarized and fully referenced our efforts at introgressing the birdsnest phenotype into both sweet and pickling melons. Backcross-pedigree breeding was used to introgress increased branching and concentrated yield into germplasm possessing high-quality, sweet fruits, including the parents of the famous ‘Galia’ hybrid. These efforts culminated in the release, in 1989, of the high-quality, concentrated-yielding muskmelon ‘Qalya’. Also, they led to the development of germplasm combining birdsnest with hermaphroditism in breeding lines of pickling melons. This germplasm has the ability to produce several times more yield than pickling cucumbers, in single- as well as multiple-harvest operations. In the future, an expected shortage of hand labor will probably result in new interest in usage of this genetic source.

A MECHANICAL HARVESTING INDEX FOR RATING THE ARCHITECTURAL CHARACTERISTICS OF BUSH-TYPE HORTICULTURAL CROPS

Plant architecture and fruit (or pod) setting habits of horticultural crops significantly influence the performance of mechanical harvesters. To better understand these affects and provide a methodology to breed and select horticultural cultivars suitable for once-over mechanical harvesting, a multi-year study using 84 commercial fields was conducted. Using the harvest loss data collected, the relationship between plant architecture of four lima bean (Phaseolus lunatus L.) cultivars and the recovery of lima beans harvested with a pod-stripper header was developed. Effect of plant architecture on header recovery was significant; cultivar M-15, which tended to set more pods in the lower zones of the plant, exhibited significantly higher harvest loss than the other cultivars. In general, greatest recovery (lowest yield loss) occurred with cultivars that set pods higher in the plant canopy. From the data collected, a mechanical harvesting index for bush-type crops that relates pod-setting architecture to header loss was established. The index can be used by plant breeders and equipment designers to select cultivars and machine configurations best suited for once-over harvest. Since previous research has demonstrated that the architecture of crops is influenced by growing conditions and practices, the harvesting index for a particular cultivar should be developed, validated, and used in the region where the crop will be grown.

Fruit Set of Triploid Watermelons as a Function of Distance from a Diploid Pollinizer

During 1998 and 1999, `Genesis' triploid watermelons [Citrullus lanatus (Thunb.) Matsum. & Nak.] were grown in large blocks with a single row of the diploid `Ferarri' planted as a pollinizer in the middle. A once-over harvest each year was made in harvest lanes 0, 1.5, 3.0, 4.5, 6.0, 7.5, and 9.0 m perpendicular distances from the pollinizer row. Individual fruit were weighed and counted. Data from both years indicated a similar distribution of triploid fruit with respect to distance from the pollinizer row. The greatest number of triploid fruit per unit land area was in the harvest row 3.0 m from the pollinizer row. When distance from the pollinizer row was 6.0 m or greater, triploid fruit numbers diminished substantially. Yield estimates made each year using the fruit density data suggested that a 1 pollinizer: 4 triploid ratio gave the maximum total triploid fruit yield per hectare for 1.5-m row spacings. These results should prove useful in designing field planting strategies to optimize triploid watermelon production.

573 Enhancing Red Color Development Without Over-ripening Apples by AVG (Aminoethoxyvinylglycine) Followed by Ethephon Treatment

AVG applied alone to `Gala' and `Jonagold' apples delayed maturity and the onset of the ethylene climacteric and delayed red color development. AVG followed by ethephon delayed maturity and the onset of the ethylene climacteric, but promoted red color development of both cultivars. Ethephon applied alone advanced maturity, ethylene production, ripening, and red color development compared to AVG alone. In other studies, the ripening-related effects of these treatments were reflected in the storability of fruit in CA storage. AVG - and AVG + ethephon-treated fruit were still at preclimacteric ethylene levels after 6 months in CA storage, with excellent retention of flesh firmness and shelf-life, while ethephon and control fruits had significantly higher ethylene levels and softened more during storage and shelf-life evaluation. Collectively, our results indicate that an ethephon application following AVG treatment may be useful to overcome the delay of red color development of apples treated with AVG only and that this can be achieved without overly stimulating fruit ripening. Thus, a once-over harvest of `Gala' and `Jonagold' apples may be achieved with a significant reduction in harvest costs. We attribute the promotion of red color development of apples receiving AVG treatment with a follow-up application of ethephon to the action of ethylene temporally-released from ethephon stimulating the development of the anthocyanin biosynthetic pathway, while AVG inhibits the development of the endogenous ethylene climacteric. Inhibiting endogenous ethylene production delays fruit from producing their own ethylene. We attribute maturation uniformity to the action of AVG allowing the less mature fruits to gain maturity while slowing maturity development of the more mature fruits. Improved storability of AVG + ethephon-treated fruit is attributed to the same ethylene-related phenomena.

231 Pollinizer Frequency for Optimum Fruit Production of Triploid Watermelons

During 1998 and 1999, `Genesis' triploid watermelons were grown in large blocks with a single row of the diploid `Ferarri' planted as a pollinizer in the middle. A once-over harvest of triploid watermelons was made each year in harvest lanes 0-, 1.5-, 3.0-, 4.5-, 6.0-, 7.5-, and 9.0-m perpendicular distances from the pollinizer row. Individual fruit were weighed and counted. Data from both years indicated a similar distribution of triploid fruit with respect to distance from the pollinizer row. The greatest number of triploid fruit per unit land area was in the harvest row 3.0 m from the pollinizer row. When distance from the pollinizer row was 6.0 m or greater, triploid fruit numbers diminished substantially. Yield estimations made each year using the fruit density data suggested that a 1 pollinizer: 4 triploid ratio gave the maximum total triploid fruit yield per hectare for 1.5-m row spacings. These results should prove useful in designing field planting strategies that seek to optimize triploid watermelon production.

029 Performance of Short-vined Tropical Pumpkins Derived from Temperate × Tropical Crosses

A joint breeding effort of the Universities of Puerto Rico and Florida involves the development of short-vined tropical pumpkin (Cucurbita moschata) genotypes that are able to reach maturity earlier than traditional long-vined types. Sixteen promising hybrids and inbreds were planted in Lajas, Puerto Rico, in June 1998. Pedigrees of this material included traditional tropical genotypes crossed with bush or compact temperate genotypes. Anthesis in both pistillate and staminate flowers occurred on average 49 days after planting. However, the variability of flowering dates among genotypes was far greater for pistillate (40 to 60 days) than staminate (46 to 54 days) flowers. Hybrids flowered earlier than inbred lines. Female flowers opened before male flowers in many genotypes. It seems likely that an inadequate source of pollen contributed to the low yields of some of the earliest genotypes. The five highest-yielding genotypes had pistillate flowers that opened after their male counterparts. All plots were once-over harvested 86 days after planting. Average yield per plant varied from 1.4 to 6.0 kg. Average fruit weight varied from 0.8 to 3.1 kg. High-yielding genotypes tended to have the highest fruit weight, a factor that should be considered when breeding for the next generation of short-vined genotypes. Yields were less than what could be expected from a long-vined tropical pumpkin. However, this yield could be obtained with a once-over harvest at about 90 days, compared to multiple harvests beginning at 120 days, saving costs of additional field practices, and allowing the land to be used for other purposes.

Testcross Performance of Three Selection Cycles from Four Pickling Cucumber Populations

Progress was measured in four populations of cucumber (Cucumis sativus L.) improved by recurrent selection. The populations were the North Carolina wide base pickle (NCWBP), medium base pickle (NCMBP), elite pickle 1 (NCEP1), and hardwickii 1 (NCH1). Families from each of three cycles (early, intermediate, and late) from each population were randomly chosen and crossed with Gy 14 to produce gynoecious hybrids. Gy 14 is a gynoecious inbred used commonly as a female parent in the production of pickling cucumber hybrids. Once the plants had 10% oversized (>51 mm in diameter) fruit, plots were sprayed with paraquat to simulate once-over harvest. Selection cycles were evaluated for total, early, and marketable yield, and fruit shape. Testcross performance for fruit shape rating increased over cycles for the NCWBP and NCMBP populations when tested in either season. Testcross performance for total and early yield of the NCEP1 population tested in the spring decreased with selection, but remained constant over cycles in the summer season. The majority of yield traits in each population remained unchanged across selection cycles. Of the four populations studied, the NCMBP population had the greatest gain (7%) in testcross performance over cycles and averaged over all traits. In addition, testcross performance for fruit shape rating had the greatest gain (11%) with selection and averaged over populations. Years and seasons greatly influenced testcross performance for fruit yield and shape rating. In most instances, the fruit yield and shape of Gy 14 was higher than the testcross performance of population-cycle combinations. The performance of several families exceeded that of Gy 14 when testcross combinations were made. Those families could be selected for use in the development of elite cultivars. Chemical name used: 1,1'-dimethyl-4,4'-bipyridinium ion (paraquat).

Little heterosis for yield and yield components in hybrids of six cucumber inbreds

Heterosis and inbreeding depression for fruit yield has been reported for pickling cucumber (Cucumis sativus L.). However, cucumber inbreds often perform as well as hybrids, and there is little inbreeding depression. The objectives of this study were to reexamine the amount of heterosis and inbreeding depression for fruit yield and yield components in pickling cucumber, and to determine the relationship between yield components and yield for heterosis. Two pickling cucumber inbreds (M 12, M 20) and inbreds from four open-pollinated monoecious cultivars (‘Addis’, ‘Clinton’, ‘Wisconsin SMR 18’, ‘Tiny Dill’) were hybridized to form four F1 hybrids (‘Addis’ × M 20, ‘Addis’ × ‘Wis. SMR 18’, ‘Clinton’ × M 12, M 20 × ‘Tiny Dill’). F1 hybrids were then self-pollinated or backcrossed to generate F2, BC1A, and BC1B progeny. Thirty plants of each generation within each hybrid family were grown in plots 3.1 m long with four replications in each of two seasons. Data were collected from once-over harvest for vegetative, reproductive, yield, and fruit quality traits. Heterosis and inbreeding depression for fruit yield and yield components were not observed in three of the hybrids. Only ‘Addis’ × ‘Wis. SMR 18’ exhibited high-parent heterosis and inbreeding depression for total, marketable, and early fruit weight. For ‘Addis’ × ‘Wis. SMR 18’, heterosis for fruit yield was associated with a decreased correlation between percentage of fruit set and fruit weight, an increased negative correlation between percentage of fruit set and both the number of branches per plant and the percentage of pistillate nodes, and an increased negative correlation between the number of nodes per branch and total fruit weight. Inbreeding depression was associated with a weakening of the strong negative correlations between percentage of fruit set and the number of branches per plant, and between the number of nodes per branch and total fruit weight. Those correlations were associated with high-parent heterosis and inbreeding depression only for one cross, and do not necessarily apply to future crosses in which heterosis may be observed for yield. We did not observe the heterosis or inbreeding depression for yield in cucumber in most of the crosses as was reported by Ghaderi & Lower (1979a; 1979c).

Performance of Three Selection Cycles from Four Slicing Cucumber Populations Hybridized with a Tester

Recurrent selection has been used as a breeding method to improve traits having low heritability such as fruit yield, earliness, and fruit shape. The objective of this study was to measure the progress of recurrent selection in four slicing cucumber populations in terms of hybrid performance when crossed with a common tester. The four populations, North Carolina wide-base slicer (NCWBS), medium-base slicer (NCMBS), elite slicer 1 (NCES1), and Beit Alpha 1 (NCBA1) populations, which differed in their genetic diversity and mean performance, were developed using modified intrapopulation half-sib recurrent selection to improve fruit yield and quality. Eleven S0 families were taken randomly from each of three selection cycles (early, intermediate, and advanced) from each population. Those families were self-pollinated to form S1 families, and the S1 families were crossed to `Poinsett 76', a popular slicing cucumber cultivar. The experiment was a splitplot treatment arrangement in a randomized complete-block design with 22 replications per population, with the four populations as whole plots and the three cycles as subplots. When 10% of fruit were oversized (>60 mm in diameter), plants were sprayed with paraquat to defoliate them for once-over harvest. Plots were evaluated for total, early, and marketable yield and fruit shape. Recurrent selection for improved fruit yield and shape per se resulted in improved hybrid performance of the NCWBS and NCBA1 populations for fruit yield and shape rating when tested in the selected or nonselected environment. The NCWBS population had the largest gain (21%) in hybrid performance averaged over all traits. In addition, early yield was improved an average of 18% from early to late cycles for each population. Even though the fruit yield and shape rating of `Dasher II' was greater than the hybrid performance of each population mean for the same traits, several F1 families within each population exceeded the fruit yield of `Dasher II'.

Optimum planting density and harvest stage for little-leaf and normal-leaf cucumbers for once-over harvest

Optimum planting density and harvest stage were determined for once-over harvest of little-leaf and normal-leaf cucumbers. Three harvest stages (10, 25, and 50% oversize fruit) and four plant densities (37,000, 75,000, 150,000, and 300,000 plants/ha) were evaluated on little-leaf cucumber (H-19) and normal-leaf cucumber (Sumter and Regal). Plant density did not affect skin color, seedcell size, and seed size in the cultivars evaluated. However, lighter skin color, larger seedcell, and larger seed size were detected at the later harvest stages in H-19. Harvest stage did not influence fruit skin color in Regal and Sumter, but seedcell size and seed size increased quadratically with harvest stage. H-19 produced the highest yield (tonne/ha) and dollar value ($/ha) followed by Regal and Sumter. Considering fruit quality and dollar value, the 10% harvest stage at 330 000 plants ha−1 was the optimum stage and density for once-over harvest of H-19 under North Carolina growing conditions. Higher yield occurred at the later harvest stages, but poorer fruit quality (increased seed and seedcell size, and a lighter skin color) was associated with those stages. Fruit quality and dollar value of Regal was best at the 10% harvest stage at approximately 240 000 plants ha−1, while 200 000 plants ha−1 was best for Sumter. Key words: Cucumis sativus, cucumber, plant type, spacing, crop ideotype, vegetable production

Economic Analysis of the Harvest-Aid Decision for Cotton in West Tennessee

Economic tradeoffs influence producers' decisions in applying a harvest-aid before a once-over or twice-over harvest for cotton (Gossypium, hirsutum L.). This decision may be affected by responses of first harvest yield and quality to the harvest-aid, cotton prices, harvest-aid treatment costs, cotton harvesting and handling costs, and weather between harvests. The objective of this study was to evaluate how these factors influence net revenues (NR) to alternative harvest-aids. Yields and fiber quality data were from a 1992 to 1994 harvest-aid study at Jackson, TN. Tbe study evaluated 12 treatments including commercial defoliants (Folex [S,S,S,tributyl phosphorotrithioate], Dropp [thidiazuron], Harvade [2,3 Dihydro-5 6-Di-methyyl 1,4-Dithiin], and Defol [sodium chlorate]) with and without a boll opener (Prep [ethephon]). Net revenues for the treatments were estimated using North Delta price quotations, harvest-aid costs, harvesting costs, and handling costs. Dropp (0.05 lb a.i./acre) and Prep (1.0 lb a.i./acre) produced the largest positive influence on effective lint price and NR for farmers interested in once-over or twice-over harvest systems. First harvest NR was significantly higher than for no harvest-aid treatment. However, a once-over harvest using this treatment would have to be delayed from the times in this experiment to allow more bolls to open to minimize second harvest NR foregone. Dropp and Prep also produced the largest two harvest NR. The most important factors influencing NR for Dropp and Prep were a low lint trash content, which resulted in a better LEAF and lower price discounts, and higher first harvest yields.

Heterosis and Inbreeding Depression for Yield of Pickling Cucumber (Cucumis sativus L.) Hybrids

Currently, both hybrid and inbred pickling cucumber cultivars are being grown commercially in the United States. Heterosis for yield in pickling cucumber has been previously reported. However, heterosis has not been repeatable in other studies. The objective of this study was to determine the existence of heterosis and inbreeding depression for yield in pickling cucumber. Six pickling cucumber inbreds (`Addis', `Clinton', M 12, M 20, `Tiny Dill', `Wisconsin SMR 18') were hybridized to form four F1 hybrid families (`Addis × M 20, `Addis' × `Wis. SMR 18', `Clinton' × M 12, M 20 × `Tiny Dill'). Within each family, F2, BC1A and BC1B generations were also formed. Thirty plants of each generation within each family were grown in 3.1-m plots for four replications in the spring and summer seasons of 1996 at the Horticultural Crops Research Station in Clinton, N.C. Data were collected at once-over harvest for total, marketable, and early yield in terms of number (1000 fruit/ha) and weight (Mg/ha). In addition to yield, a fruit shape rating was collected for each plot. High parent heterosis for yield (total and marketable fruit weight) was only observed for `Addis' × `SMR 18' grown in the summer season. The three other families did not exhibit heterosis for total, marketable, and early yield. Heterosis for shape rating was not observed for any family. `Addis' × `Wis. SMR 18' also exhibited inbreeding depression for total fruit weight, marketable fruit weight, early fruit number, and early fruit weight during the spring season and for marketable fruit number and marketable fruit weight during the summer season.

Use of Ethephon as a Controlled Abscission Agent on Paprika Pepper

Mechanical harvest of paprika pepper (Capsicum annuum L.) produces a mixture of marketable and unmarketable fruit. Our objective was to increase the percentage of marketable red fruit in a once-over harvest by using ethephon to remove late-developing flower buds, blooms, and green fruit. Three experiments were conducted on field-grown plants in southwestern Oklahoma. We tested ethephon solutions of 0, 1000, 2000, 3000, and 4000 μL·L-1 as a one-time foliar application on various dates in September and October. Total dry mass of harvested fruit decreased linearly as ethephon rate increased in all experiments. Marketable fruit, as a percentage of total harvested fruit mass, increased linearly with ethephon rate in two of three experiments. Ethephon decreased the percent of total harvested fruit mass due to green fruit in all experiments. We recommend a single application of ethephon at about 2000 to 3000 μL·L-1 as a controlled abscission agent to increase the percentage of harvested red fruit in paprika pepper. The precise timing of the application will vary with the situation, but the last 10 days in September seemed an appropriate interval for southwestern Oklahoma. Chemical name used: (2-chloroethyl)phosphonic acid (ethephon).

RECURRENT SELECTION FOR SPECIFIC COMBINING ABILITY FOR YIELD IN FOUR SLICING CUCUMBER POPULATIONS

Plant breeders often measure selection progress for yield by measuring the hybrid performance (combining ability) of a breeding line. This information is used to develop breeding lines with higher combining ability. The objectives of this study were to measure the specific combining ability for yield traits over three selection cycles from four slicing cucumber populations with `Poinsett 76', a popular slicing cucumber cultivar; and to determine the change in specific combining ability for yield traits in four populations improved through recurrent selection. Four slicing cucumber populations, North Carolina wide base slicer (NCWBS), medium base slicer (NCMBS), elite slicer 1 (NCES 1), and Beit Alpha 1 (NCBA1), were developed and improved through modified half-sib selection from 1983 to 1992 to improve yield per se and fruit quality in each population. Eleven families were randomly selected from each of three selection cycles (early, intermediate, advanced) from each population and were hybridized to `Poinsett 76'. Twenty-three seeds from each cross were planted in 1.2-m plots in Spring and Summer 1995. When 10% of fruit were oversized (>50 mm in diameter), plants were sprayed with paraquat to defoliate them and to simulate once-over harvest. The experimental design was a randomized complete block with 22 replications per population arranged in a split plot with the four populations as whole plots and the three cycles as subplots. The combining ability for early and marketable yield of NCWBS and NCBA1 increased as the number of selection cycles increased. Conversely, selection for higher yield per se decreased the combining ability of the NCES 1 population for early and marketable yield. The NCBA1 population exhibited the largest gain (131.2%) from cycle 0 to 8 averaged over all traits. Early yield exhibited the largest gain (60.8%) averaged over all populations.

Plant Population and Spacing Effects on Processing Tomato Growth and Yield

Processing tomato (Lycopersicon esculentum Mill.) producers in the Great Lakes region have expressed interest in cutting crop establishment costs and improving profitability by reducing plant populations. This study compared plant development, fruit set, fruit size and yields using a range of single and twin-row plant populations (14,800 to 44,500 plants/ha) and four commercially important processing tomato cultivars (`OH8245', `H9036', `PS696', and `H7135') with differing vine types and maturities. The 3-year study was conducted at Fremont, Ohio, on a Colwood fine sandy loam, using raised beds and other standard cultural practices. Six- to seven-week-old transplants (288 cell size) were mechanically planted in middle to late May. Once-over harvest was timed to achieve 80%–90% red fruit, using a Johnson tomato harvester. Plant population had a significant effect on 1995 fruit yields for all cultivars tested. Optimum red fruit yields were observed at 37,100 plants/ha in twin-rows for `OH8245', which was similar to 1994 results. Optimum fruit yields for `PS696' were obtained at twin-row populations of 29,600-44,500 plants/ha in 1995. Three year results for `OH8245' (medium-sized vine) indicate no significant differences due to plant population or arrangement. Mean red fruit yields varied considerably by year in this field research (62.7, 95.2, and 44.8 MT/ha in 1993, 1994, 1995 respectively), but twin-row spacing of `OH8245' provided significant yield gains in 2 of 3 years for populations of 29,600 plants/ha or greater.