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Steven A. Fennimore, Frank N. Martin, Thomas C. Miller, Janet C. Broome, Nathan Dorn and Ian Greene

Steam-disinfestation of soil as an alternative to chemical fumigation was investigated in both research and commercial strawberry (Fragaria ×ananassa Duch.) production field trials at four sites over 2 years (2011–13) using new prototype commercial application equipment: a tractor-drawn device that physically mixed the steam with the soil as it passed through the shaped planting beds. Results included significant suppression of weeds and soilborne pathogens equal to commercial chemigation of chloropicrin with 1,3-dichloropropene (Pic-Clor 60). Also, the combination of steam treatment with soil amendments of mustard seed meal (MSM; two of four trials included treatment), a fertilizer and source of additional organic matter, showed very favorable strawberry production in terms of yield as well as weed and pathogen control. Soil nitrogen-containing ions were monitored at two of the sites and the MSM treatment significantly elevated available soil nitrates by the time of transplanting as did the steam treatment alone, but only significantly at one of the sites.

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Anna L. Hale, Douglas C. Scheuring, Thomas J. Gerik, Jeffrey D. Hart and J. Creighton Miller Jr.

Iron Deficiency Chlorosis (FeDC) is a problem in cowpea because it affects the ability of the plant to produce chlorophyll. Earlier studies indicated that FeDC was conditioned by a single gene. Pinkeye Purple Hull (PEPH), a susceptible variety, and Texas Pinkeye Purple Hull (TXPE), a resistant variety, were crossed and allowed to self for one generation. The F1s were backcrossed to the parents. SPAD readings were taken on each population. SPAD measures the transmission of light through the leaves at a wavelength where chlorophyll absorbs and a wavelength where it does not. The SPAD reading is calculated based on a ratio of these two numbers. Thus, the SPAD value is unitless and is an indication of the relative amount of chlorophyll present in the leaf. Chlorophyll was extracted from leaves, and regressed on the SPAD readings from the same leaves. An R 2 of .9102 was obtained as well as a regression equation of y = 12.8x + 54.5. Thus, a SPAD value of 1 corresponds with a chlorophyll content of ≈67.3 μg chlorophyll/gfw. The data was analyzed using a bootstrap method, and indicated that FeDC is not controlled by a single gene. A P-value of .0004 showed a highly significant difference between the expected and observed segregation ratios in the F2 plants. Narrow sense heritibility (Mather) was estimated at 0.3.

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H.M. Cortinas-Escobar, Douglas C. Scheuring, Thomas J. Gerik and J. Creighton Miller Jr.

Cowpea [Vigna unguiculata (L.) Walp.] cultivars differ in their response to iron deficiency when grown on calcareous soils. This response is influenced by environmental factors such as soil pH, soil texture, presence of bicarbonates, and temperature. The objective of this study was to determine the genetic basis for resistance to iron deficiency in cowpea. Crosses of `Texas Pinkeye Purple Hull' (resistant) and `Pinkeye Purple Hull' (susceptible) were made in the greenhouse during Spring 1994, and F2 seeds were obtained in the summer. Reciprocal crosses were made in order to test for maternal effects. Seed of the parental, F1, and F2 generations were planted near Temple, Texas, during Fall 1994. The color (greenness) of 1031 F2 plants was measured using a chlorophyll meter (Minolta SPAD-502) 35 days after planting. Chi-square analysis showed a good fit to a 3:1 ratio of susceptible: resistant plants. These results suggest simple inheritance of the response to iron deficiency in cowpea. Similar segregation of the reciprocal crosses indicated absence of maternal inheritance.

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H.M. Cortinas-Escobar, Douglas C. Scheuring, Thomas J. Gerik and J. Creighton Miller Jr.

Dry bean (Phaseolus vulgaris L.) cultivars differ in their response to iron deficiency when grown on calcareous soils. This response is influenced by environmental factors such as soil pH, soil texture, presence of bicarbonates, organic matter, and temperature. The objective of this study was to investigate the genetic basis for resistance to iron deficiency in beans. Crosses between nine resistant and three susceptible cultivars/lines were made in the greenhouse during Spring 1994, and F2 seeds from 12 different crosses were obtained in the summer. Seed of the parental and F2 generations were planted near Temple, Texas, during Fall 1994. The color (greenness) of 1482 F2 plants was measured using a chlorophyll meter (Minolta SPAD-502) 35 days after planting. Chi-square analysis showed a good fit to a 15:1 ratio of resistant: susceptible plants. The F2 segregation suggests that two dominant genes are involved in the response to iron deficiency in dry beans, and when either dominant gene is present, resistance is expressed to some degree.