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Daniel I. Leskovar and Ronald R. Heineman

This study was conducted to investigate how irrigation systems alter root elongation, root morphology, shoot growth characteristics and yield of `TAM-M' jalapeno pepper seedlings. Transplants were grown in containerized trays (18 cm3/cell) for 6 weeks in a greenhouse in Spring 1991. Irrigation systems were: a) floatation (FI), b) 4-week floatation plus 2-week overhead (FI+OI); c) alternate floatation and overhead (FI/OI), and d) overhead (OI). The growing media was maintained between 50 and 20% of its water holding capacity. Between 20 and 41 days after seeding (DAS), FI and FI/OI transplants maintained a constant lateral root length increase. In both FI+OI and OI transplants, lateral root elongation response tended to a `plateau' at ≈ 31 DAS. However, between 31 and 41 DAS, OI transplants had a root growth compensation, increasing the number and length (33%) of basal roots. In FI+OI transplants, basal root growth compensation occurred later in the field. At planting, OI transplants had higher shoot/root ratio (S:R=5) and maintained a higher shoot water potential (ψ= -0.58 MPa) than FI transplants (S:R=3; ψ= -0.69 MPa), respectively. Overhead-irrigated transplants had higher early fruit yields than floatation-irrigated transplants, but total yields were unaffected.

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Maria A. Macias-Leon and Daniel I. Leskovar

Onions (Allium cepa L.) are easily outcompeted by weeds because of slow germination and relative growth rates. Therefore, high percentage of seed germination and root vigor are important traits to improve field performance. The effects of exogenous plant growth regulators (PGRs), 2-chloroethylphosphonic acid (ethephon, Eth), indole-3-acetic acid (IAA), trans-zeatin (tZ), and 1-aminocyclopropane-1-carboxylic acid (ACC) were evaluated on the germination and root growth of ‘Don Victor’ (yellow) and ‘Lambada’ (red) onion seedlings. Seeds were soaked for 10 hours in hormonal solutions and water (hydro-priming). Seed germination improved with Eth (30 and 100 μm), Eth (100 μm) + IAA (10 μm), and IAA (3 μm) treatments. Root surface area (RSA) increased in response to Eth at 30 and 100 μm, Eth + IAA, and 3 μm IAA. Root length (RL) and root diameter (RD) were enhanced by 1 μm tZ and 100 μm ACC. Eth reduced RL and RD, whereas IAA showed no effects. A subsequent experiment evaluated synergistic effects of different PGRs. Treatment of seeds with ACC (250 μm) + tZ (0.5 μm) and ACC (250 μm) + tZ (0.5 μm) + Eth (20 μm) enhanced RL and RD. RSA was unaffected by ACC + tZ + Eth. The results suggest that exogenous PGRs could be useful to enhance germination, RL, and RSA of onion seedlings.

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Jose R.A. Santos and Daniel I. Leskovar

Poor seedling emergence and stunted growth were observed in cauliflower (Brassica oleracea L., Botrytis group) and cabbage (Brassica oleracea L., Capitata group) crops when planted after three consecutive monocrops of broccoli (Brassica oleracea L., Italica group). This study was conducted to assess seed, seedling, and plant growth responses of broccoli, cabbage, and cauliflower to broccoli residue (leaves, stem + roots, and whole plant) extracts, broccoli residue incorporation, or soil previously cropped to broccoli. Osmotic potential, electrical conductivity, and pH of extracts were measured, rate (T50) and total germination were determined. Filter-sterilized leaf extract delayed T50(7.5 d) and reduced total germination (22%) of cauliflower compared to broccoli or cabbage. Similarly, plant height, shoot dry weight, and leaf area of cauliflower were significantly reduced when grown on broccoli soil in the greenhouse. Cabbage and cauliflower had low total marketable yields with more culled heads when grown in the field previously cropped to broccoli. Therefore, a potential growth inhibition of cabbage and cauliflower exists when following a continous cropping of broccoli.

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Daniel I. Leskovar, Chenping Xu, and Shinsuke Agehara

Globe artichoke is typically grown in Mediterranean and coastal areas. Because of the high profitability as a specialty crop, demand to develop production systems optimized for other semiarid and water-limited regions is rising. Field experiments were conducted over three seasons (2008–09, 2010–11, and 2011–12) in southwest Texas to investigate plant growth, physiology, and yield of artichoke grown as an annual system. Three strategies were evaluated: planting configuration (single and double lines per bed), plasticulture (bare soil and black plastic mulch), and cultivars differing in maturity (‘Imperial Star’, early; ‘Green Globe Improved’, late). Each fall, transplants were established in the field at 2.03 m between rows and 0.90 m between plants (single line) or 4.06 m between rows and 0.90 m between plants (double line). In both cultivars, black plastic mulch enhanced plant growth (leaf number, plant height and width) and increased early yield; however, its effect on total yield and yield components was not consistent. Single line per bed significantly increased head number of jumbo and large size per plant as compared with double line in the 2009 season. Chlorophyll index was unaffected by either planting configuration or plastic mulch. Comparing cultivars, ‘Green Globe Improved’ had lower marketable yield but bigger head size than ‘Imperial Star’ in one and two seasons, respectively. Our results indicate that single line with black plastic mulch can be recommended to improve earliness and water savings as compared with the bare soil system for annual artichoke production.

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Daniel I. Leskovar and Peter J. Stoffell

Initiation, development, and subsequent growth of seedling root and shoot components can have a direct influence on the quality, adaptation, and survival of seedlings, particularly under stress conditions. Taproot, basal, lateral, and adventitious root components (common indicot plants) each have their own development sequence, growth rate, and may have separate functions for subsequent seedling growth and development. Stresses originating in root components may be expressed in shoots affecting dry matter partitioning between roots and shoots. Partitioning and development of root morphological components and root/shoot growth adaptation to stress environments will be presented for various vegetable species. Implications of root developmental differences in relation to field planting methods will be discussed. Understanding seedling morphology, physiology and assimilate partitioning during early ontogeny would assist directing strategies to improve field establishment and ultimately crop production.

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Brian A. Kahn and Daniel I. Leskovar

Studies were conducted to examine the effects of pruning treatments applied to spring-transplanted bell peppers (Capsicum annuum L.) on marketable fruit yield in late summer and fall. Control plants were set in the field in early May 1997 (Oklahoma) and Apr. 1998 (Oklahoma and Texas) and were harvested weekly into October (Oklahoma) or periodically into December (Texas). In 1997, there were no differences in total marketable fruit weight among four treatments involving height and method of pruning, but all reduced total marketable fruit weight relative to the control. In Oklahoma in 1998, the control was compared to plants mowed on 27 July at an average height of ≈24 cm. Mowed plants produced less total marketable fruit weight but more U.S. Fancy fruit than control plants. Also, control and mowed plants did not differ in weight of U.S. no. 1 fruit. In Texas in 1998, the control was compared to plants mowed on 4 Sept. at a height of ≈20 cm. Mowed plants produced more than double the weight of U.S. no. 1 fruit and fewer cull fruit than control plants. Nonpruned transplants set in the field in Summer 1998 (Oklahoma and Texas) gave low marketable yields. Maintaining spring-transplanted bell peppers is a viable technique for fall pepper production, and the highest total marketable yields may occur if these plants are not mowed. However, mowing offers an opportunity for increased fall production of premium fruit, and mowed plants would be easier to manage than unpruned plants.

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Daniel I. Leskovar and A. Kipp Boales

Azadirachtin (ATI), an insect growth regulator derived from extracts of neem (Azadirachta indica A. Juss) seed, was evaluated for the control of cabbage looper (Trichoplusia ni Hübner), diamondback moth (Plutella xylostella L.), and silverleaf whitefly (Bemisia argentifolii Bellows and Perring) in cabbage (Brassica oleracea L. Capitata Group) grown in southwestern Texas. In Fall 1992, ATI was tested with the a.i. at 0, 22, 33 and 44 g·ha–1. In 1993, ATI was evaluated at 33 g·ha–1 and in combination with M-Pede (1%, v/v), an organic insecticide based on potassium salts of fatty acids at 49%. Two commercial (Align and Neemix) and one experimental hydrogenated (LDF) ATI formulations were evaluated at 11 g·ha–1 in 1994. Insect populations were monitored weekly before and after treatment application. Plant damage was evaluated immediately before harvest, and marketable yields were determined. In 1992, large (>6 mm long) and total cabbage looper counts were reduced by ATI compared with the nontreated control. Insect mortality was similar for all ATI rates tested in 1992. In 1993, ATI at 33 g·ha–1 + M-Pede reduced the number of cabbage looper and diamondback moth larvae. ATI efficacy against cabbage looper and diamondback moth was enhanced when crop oil (polyol fatty acid esters with polyethoxylated derivatives) was tank-mixed with Align or LDF formulations in 1994. ATI did not reduce the number of silverleaf whitefly nymphs compared to the control. In all seasons, ATI-treated plants had lower insect-induced plant damage and higher marketable head weights than the nontreated control. Using ATI on lepidopterous pests appears to be beneficial for integrated pest management strategies.

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Daniel I. Leskovar and A. Kipp Boales

Seed production systems for daikon or Chinese winter radish (Raphanus sativus L., Longipinnatus Group) were investigated in the Winter Garden of southwest Texas in 1992 and 1993. Planting dates ranged from October through March. Bed configurations (number of rows × bed spacings) were 2 × 0.96 m, 2 × 1.93 m, 3 × 1.93 m, and 4 × 1.93 m. Within-row spacings were 5, 10, and 15 cm. Crops were grown using minimum fungicide and insecticide amounts, while no attempt was made to control weeds chemically. Seed was harvested between May and June. Seed yields (kg·ha–1) increased for planting dates of October to November. Lower seed yields from the January or later plantings appear to be related to increased disease and insect pressures. Total and medium class size (≥3 and ≤4 mm in diameter) seed yields were highest at 40 rows × 1.93 m bed spacings and 10 cm within-row plant spacings. Germination and percent coatless seeds were unaffected by bed configuration and within-row plant spacings. The closest within-row spacings (5 cm) increased the risk of plant lodging and delayed plant maturity.

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Daniel I. Leskovar and Peter J. Stoffella

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Brian A. Kahn and Daniel I. Leskovar

Studies were conducted to examine the effects of pruning treatments applied to spring-transplanted bell peppers (Capsicum annuum L.) on marketable fruit yield in late summer and fall. Control plants were set in the field in early May 1997 (Oklahoma) and Apr. 1998 (Oklahoma and Texas) and harvested weekly into October (Oklahoma) or periodically into December (Texas). In 1997, all four treatments (involving height and method of pruning) reduced total marketable fruit weight, but differences among treatments were nonsignificant. In Oklahoma in 1998, plants were mowed on 27 July at an average height of ≈24 cm. Mowed plants produced less total marketable fruit weight but more U.S. Fancy fruit than did control plants, while weight of U.S. No. 1 fruit was not affected. In Texas in 1998, plants mowed on 4 Sept. at a height of ≈20 cm produced more than twice the weight of U.S. No. 1 fruit and fewer cull fruit than did control plants. Nonpruned transplants set in the field in Summer 1998 (both Oklahoma and Texas) produced low marketable yields. Maintaining spring-transplanted bell peppers is a viable technique for fall pepper production, and the highest total marketable yields may be obtained if these plants are not mowed. However, mowing offers an opportunity for increased fall production of premium fruit, and mowed plants would be easier to manage than nonpruned plants.