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Sharon J. Keeler, John J. Frett, and Sherry L. Kitto

Heat stress on field grown Phaseolus lunatus (lima bean) can have a significant influence on yield. Lima bean crops grown in Delaware typically yield less pounds per acre than the same cultivars grown in California. Part of this effect may be due to extreme heat conditions or fluctuations during Delaware's summers, which can affect blossom and pod set. Our purpose was to analyze the heat tolerance of various cultivars of P. lunatus using quick bioassays and to establish a relationship to yield in greenhouse temperature trials. Two assays were used. The first, a hypocotyl extension assay, consisted of a treatment of germinated seedlings at 25, 35, or 42 for 2 h and observations of hypocotyl extension at 72 and 96 h posttemperature treatments. Three cultivars [`Fordhook' 1072 (heat-sensitive), `Jackson Wonder' (heat-tolerant), and `Early Thorogreen' (heat tolerant)] were analyzed. Initial results indicated that `Jackson Wonder' and `Early Thorogreen' are capable of surviving the 42C heat shock, but `Fordhook 1072' is not. In the second assay, we measured electrical conductivity of a solution containing hypocotyl sections following incubation at various temperatures (R1). Tissue samples then were boiled and conductivity was measured again (R2). The ratios of R1/R2 × 100 were determined as percent injury. Preliminary data suggests that `Jackson Wonder' is more heat-tolerant in this assay than `Fordhook 1072'. Subsequent experiments will analyze the induction of specific heat shock proteins as a function of cultivar-specific heat tolerance.

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Edwin Kee and De James L. Glancey

Mechanical pod strippers are the predominant method of harvesting lima beans (Phaseolus lunatus L.) for processing. Field losses are high, averaging 20% of potential yield in over 90 tests conducted in commercial fields. The three most significant factors that affect lima bean recovery are the field levelness, the relationship between ground speed and picking reel speed, and the lima bean variety. Further study on the relationship between pod location of four lima bean cultivars and the recovery of lima beans harvested with pod stripper combines was conducted in commercial fields. Pod location was categorized into three distinct zones of the plant. These three zones represented pods falling below the point the mainstem comes out of the ground, the first 5 cm from that point up the main stem, and all other pods higher than 5 cm above the stem. Differences in four cultivar's habits of setting pods in the three zones were established. `M-15' placed more pods in the lower zones than other cultivars. `M-15' also exhibited consistently more harvest loss than other cultivars when harvested with pod stripper combines. Other cultivars set pods higher in the plant and exhibited less harvest loss. With the harvest loss and pod set data, a rating procedure for the harvestability of lima beans was explored. While several potential rating systems demonstrated strong correlation with harvest loss data, a simple rating based on the percentage of pods in the canopy of the plant had the highest correlation coefficient (r = 0.96) with harvest loss. New cultivars can be evaluated for their harvestability characteristics using this rating system.

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Kathryn R. Kleiner and John J. Frett

A greenhouse study was designed to determine the relative heat tolerance of 10 lima bean cultivars and to evaluate the effects of high temperature on lima bean yield. Cultivars were arranged in a randomized complete block with three blocks per treatment. The temperature treatments were 25C day/15C night and 35C day/25C night. Cultivars varied in their response to the higher temperature, allowing for classification into three heat response groups: intolerant, average, and tolerant. Heat-intolerant plants did not experience a significant reduction in number of pods, but number of beans and total bean weight were reduced at the higher temperature. Number of seeds per pod and average weight per bean also tended to decrease in intolerant plants at 35C. In future experiments, these data will be correlated with random amplified DNA (RAPD) markers. These markers will be evaluated for their potential for heat tolerance screening.

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Yacob Sirait, Wallace G. Pill, and Walter E. Kee Jr.

`Maffei-15' lima beans were subjected to three irrigation regimes (natural rainfall only, partial = 50 mm each week of rain or irrigation from first-flower bud to harvest, and full = 50 mm each week of rain or irrigation from planting to harvest), two between-row spacings (38 and 76 cm), and two in-row plant spacings (5 and 10 cm). The wider in-row spacing increased individual plant vegetative growth but had no effect on economic yield. The combination of 38-cm rows and partial irrigation provided the highest crop growth rate, plant dry matter, leaf area index, water-use efficiency, and economic yieid (equivalent to 3.3 t·ha-1).

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H.T. Erickson

Indeterminate growth habit in lima bean is inherited as a single gene dominant. A qualitative short-day photoperiodic response for flowering appears to be controlled by duplicate dominant genes with coupling linkage to the gene for growth habit. Partial epistasis of the determinate growth habit on genes for short-day response is suggested.

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Mathew Wilson and Jeffrey C. Wong

The Fordhook lima bean is a large-seeded lima bean grown in California for use by vegetable processors as an ingredient in frozen mixed vegetable packs. California represents one of the largest production regions for this bean because of the temperate climate. Unfortunately, as the population of California grows, the land available for producing this relatively low-valued crop continues to diminish. To overcome the loss of productive lands, we have initiated two projects, both focused on an increase in productivity. The first project is the improvement of current lines used by one processor. Due to the method of production of the seed bean, as well as the age of current lines in use, plant vigor and uniformity within the fordhook lima bean population has decreased over time. By using a modified single-seed descent method within the population, a certain level of improvement of production lines should be realized. Our second objective is in the development of a more heat-tolerant line, which could be grown in the inner valleys of California, where more land is available. Because of the limited availability of heat-tolerant Fordhook lima beans, we are currently investigating the possibility of using chemical mutagenesis to produce a more heat-tolerant variety.

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James Nienhuis, Jan Tivang, Paul Skroch, and Joao B. dos Santos

Knowledge of relative genetic distance among genotypes is useful in a breeding program because it permits organization of germplasm resources. Genetic distance (GD) was estimated among 65 Phaselous lunatus L.. accessions, which included 4 large-seeded and 7 small-seeded cultivars and 54 germplasm accessions (landrace's) from the Caribbean and North, Central, and South America. Based on 125 polymorphic random amplification polymorphic DNA (RAPD) bands, two major clusters, which generally correspond in seed size and geographic region to [be Mesoamerican and Andean gene pools, were observed among the landraces (GD = 0.726 ± 0.041). Four Fordhook cultivars and a landrace from the United States formed a separate cluster that is more distantly related to the small- (GD) = 0.561 ± 0.039) than to the large-seeded cluster (GD = 0.303 ± 0.022). The mean GD between the Andean and Mesoamerican (0.726), Mesoamerican and Fordhook (0.561), and Andean and Fordhook (0.303) clusters were all significant. The significant GD between the Andean and Mesoamerican groups supports the hypothesized existence of two major gene pools in lima bean. The RAPD marker diversity of the Mesoamerican group was the largest (0.1 10), followed by the Andean (0.097) and Ford hook (0.062) groups. The plot of the relationship between the coefficient of variation (cv) and sample size (number of bands) indicates that cvs as low as 10% for estimating CD between Andean and Mesoamerican lima bean accessions can be achieved by sampling as few as 100 bands.

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Luisa Santamaria, Emmalea G. Ernest, Nancy F. Gregory, and Thomas A. Evans

Delaware and the mid-Atlantic Region Plant Dis. 91 128 135 Evans, T.A. Mulrooney, R.P. Santamaria, L. 2005 Development of races of Phytophthora phaseoli , the causal agent of downy mildew of lima bean ( Phaseolus lunatus ) and the development of resistance

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Xuan Liu and Donald L. Suarez

exchange study may reveal more information for our understanding of how leaf photosynthetic performance responds to salt stress. Lima bean ( Phaseolus lunatus ) is an internationally important legume and a major crop in several regions, and its annual

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Andrew M. Birmingham, Eric A. Buzby, Donte L. Davis, Eric R. Benson, James L. Glancey, Wallace G. Pill, Thomas A. Evans, Robert P. Mulrooney, and Michael W. Olszewski

A mechanical planter was developed to sow seed of baby lima beans (Phaseolus lunatus) in small plots. The mechanical seeder allowed small plots to be quickly and consistently seeded at a fixed spacing. Seeds were manually spread along a 10-ft (3.0 m) base plate containing 50 holes of slightly larger diameter than the seed length and at the desired seed spacing [2.4 inches (6 cm)]. Once all the holes were filled, a slider plate below the base plate containing holes of the same diameter and spacing, but which were slightly offset, was slid horizontally so that the holes of the base and slider plates aligned and the seeds dropped to the bottom of the furrow. Compared to manual planting, the mechanical planter increased the precision of seed placement and reduced the time needed to plant 50 seeds. The planter was easy to use and transport, and was inexpensive.