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- Author or Editor: Robert R. Coltman x
Abstract
Root culture was adapted for screening a diverse collection of tomato (Lycopersicon esculentum Mill.) strains for tolerance to low supplies of P. Fifty-one tomato strains were screened in 10 consecutive experiments for root fresh weight (RFW) production with high non-growth-limiting (25 μm) and low growth-limiting (7 μm) concentrations of P in a sterile, liquid medium. Twenty strains showing the most and least restricted root growth at low P in the initial 10 experiments were grown simultaneously in three final screening experiments. Restrictions in RFW at low P averaged 51% for four strains, consequently classed as low-P “intolerant”, and averaged 27% for three strains, consequently considered low-P “tolerant”. At high P, RFW of tolerant strains averaged 17% less than RFW of intolerant strains. At low P, RFW of tolerant strains averaged 23% greater than RFW of intolerant strains. The greater RFW production of intolerant strains at high P was due to higher internal P use ratios (IPUR = mg root dry weight (RDW) per mg P adsorbed). Differences in growth at low P were due primarily to differences in P uptake. However, the relative contributions of P use and P uptake efficiencies to low-P tolerance were different among strains. Root hairs of tolerant strains at low P were longer and covered a greater proportion of the root length than root hairs of intolerant strains. The pH of the culture medium of one tolerant strain was significantly lower than the medium pHs of the other strains.
Abstract
‘Caruso’ tomatoes (Lycopersicon esculentum Mill.) were grown in peat-perlite-vermiculite in a greenhouse with five nitrate-nitrogen (NO3-N) fertilization concentrations in irrigation waters managed to maintain 200, 400, 600, 900, or 1200 µg NO3-N/ml in petiole sap as determined by weekly NO3-N quick tests. Nitrate-N fertilization concentrations immediately were increased 50% when petiole sap NO3-N levels first fell below these target levels; thereafter, NO3-N fertilization concentrations were increased only after petiole sap levels fell below target levels for 2 consecutive weeks. The critical target level of sap NO3-N was defined as the lowest petiole sap NO3-N target level producing maximum marketable fruit yields. Total fruit yields increased with increasing petiole sap NO3-N target levels through 1200 µg·ml–1. Marketable fruit yields were maximized at 3.2 kg/plant, with an estimated critical sap NO3-N target level of 1105 µg·ml–1. Application of the sap NO3-N management rules used in this experiment resulted in five adjustments in N fertilization concentrations over the 27-week crop cycle, with an average of 4.5 weeks between adjustments. This approach to the management of N fertilization based on the sap NO3-N level of the crop has potential to provide significant benefits in improved N use and crop productivity at a modest cost.
Abstract
Tomato plants were grown in two greenhouse experiments to determine sampling guidelines for using semiquantitative quick tests of petiole sap nitrate to monitor crop N status. In Expt. 1, a 40-µg NO3-N/ml liquid feed rate produced maximum marketable yields of ‘Celebrity’ tomatoes (Lycopersicon esculentum Mill.) (3.4 kg/plant) with estimated petiole sap concentrations of 2138, 1091, and 636 µg NO3-N/ml at early bloom, small fruit, and full-ripe fruit stages, respectively. In Expt. 2, a stable minimum level of petiole sap NO3-N of about 800 µg·ml−1 was found during fruit production in maximally yielding (3.1 kg/plant) ‘Tropic’ tomato plants. These plants received 60 µg NO3 − N/ml in liquid feed solutions during fruit production. Liquid NO3-N feed rates producing maximum yields in these experiments were about five times lower than those typically used for growing tomatoes. Sap nitrate content did not fluctuate greatly between 0803 hr and 1430 hr. Sap nitrate levels rose sharply in response to increased N feed concentrations and as a result of lower leaf pruning. Because of high day-to-day and plant-to-plant variation in petiole sap nitrate readings, strategies for obtaining results with sufficient diagnostic value would appear to involve at least weekly samplings of five to 15 plants, and restricting diagnoses of deficient crop N to instances where readings < 800 µg NO3-N/ml for two or more consecutive samplings have been obtained.
`Celebrity' tomatoes (Lycopersicon esculentum Mill.) were grown in peat–perlite under greenhouse conditions in two experiments with five levels of K (25, 50, 100, 200, and 300 mg·liter–1) in irrigation waters. In both experiments, aqueous petiole sap K concentrations (milligrams K per milliliter) were monitored weekly with colorimetric paper test strips. Variation in petiole sap K concentrations among plants was low among three-plant replicates (cvs of 9% to 11%). Petiole sap K concentrations varied considerably from week to week, but remained relatively constant over time at levels determined by external-feed K concentrations. Petiole sap K levels and marketable-fruit yield increased quadratically with increasing external K concentrations. Maximum yields were produced with 190 to 200 mg K/liter in external-feed solutions. Maximum marketable yields of ≈2.75 kg/plant occurred with =5.9 mg K/ml in petiole sap. Quick petiole sap K tests appear to be suitable for assessing the K status of greenhouse tomatoes.
`Waimanalo Long' eggplant (Solanum melongena L.), `Kahala' soybean [Glycine max (L.) Merrill], `Jumbo Virginia' peanut (Arachis hypogea L.), `Waimanalo Red' sweet potato [Ipomea batatas (L.) Lam.], and `Green Mignonette' semihead lettuce (Lactuca sativa L.) were field-grown in two seasons at Waimanalo, Oahu, Hawaii, in the open sun and with four artificially produced levels of shade (30%, 47%, 63%, and 73%). Yields and vegetative growth of eggplant, soybean, peanut, and sweet potato decreased linearly with increasing shade levels. Compared to unshaded controls, yields of semihead lettuce increased significantly under 30% shade in Fall 1986. During Spring 1987, lettuce yields were reduced only slightly from unshaded levels by increasing shade up to 47%. Leaf areas of index leaves of eggplant, soybean, and lettuce were similar to unshaded controls as shade intensity increased, while leaf dry weight decreased under shade. By comparison, both leaf area and leaf dry weight of peanut index leaves decreased as shade increased. Leaf area and leaf dry weight of sweet potato did not respond to shading. The results indicate that, of the five crops studied, only lettuce can be grown successfully under lightly shaded conditions and still receive enough radiant energy for maximum photosynthesis and yields.
`Green Mignonette', `Salinas', `Parris Island Cos', and `Amaral 400' lettuce (Lactuca sativa L.); `WR-55 Days' Chinese cabbage (Brassica rapa L. Pekinensis Group); Waianae Strain' green mustard cabbage [Brassica juncea (L.) Czerniak]; `Tastie Hybrid' head cabbage (Brassica oleracea L. Capitata Group); and an unnamed local selection of green bunching onions (Allium fistulosum L.) were field-grown during Fall 1987 and Spring 1988 at Waimanalo, Oahu, Hawaii, in full-sun and with four artificially produced levels of shade (30%, 47%, 63%, and 73%). Yields of cos lettuce, green mustard cabbage, and green bunching onions were irresponsive to shade or negatively affected by shade in both seasons. Yield responses of the other crops to shade varied seasonally. Optimum shading of 30% to 47% increased `Green Mignonette', `Salinas', and `Amaral 400' lettuce yields by 36% and head cabbage and Chinese cabbage yields by 23% and 21%, respectively, compared to full-sun plots in one or both seasons. Leaf areas similar to unshaded controls were maintained as shade intensity increased, while leaf dry weight decreased in all crops except `Salinas' and `Parris Island Cos' lettuce. Maximum rates of net photosynthesis (Pn) were attained at 1500 umol·s-1·m-2, which was about two-thirds of full sunlight.
Abstract
Responses of bell peppers (Capsicum annuum L.) to inoculation with the vesicular–arbuscular mycorrhizal fungus (VAMF) Glomus aggregatum (Schenck and Smith emend Koske) were examined under greenhouse and field conditions. Inoculation did not affect tissue P concentrations, growth, or yields in “high”-P soil (0.30 mg P/liter of soil solution) in either the greenhouse or field. In “low”-P soil (0.03 mg P/Iiter), inoculation increased tissue P concentrations, plant weights, and fruit yields relative to noninoculated plants. Tissue P concentrations increased more rapidly after transplanting when seedlings were inoculated at seeding than when inoculation was delayed until transplanting. In the field, total fruit yields and final shoot fresh weights also were higher when transplants were inoculated before transplanting. Water stress reduced fruit yields of plants growing in P-deficient soil less if they were inoculated than if they were not inoculated.
Abstract
Growth, shoot P concentrations, and vesicular-arbuscular mycorrhizal infection by Glomus aggregatum (Schenck and Smith emend. Koske) were studied on transplants of bell pepper (Capsicum annuum L. ‘Emerald Giant’) and leek (Allium ampeloprasum L. ‘Catalina’) grown in a 1 peat : 1 vermiculite medium (v/v). Various amounts of Osmocote (19N–2.6P–10K) were added to the transplant medium, resulting in solution P concentrations of 0.6 to 17.5 mg·liter–1. The transplants received 0 to 12,500 spores of G. aggregatum per plant. Increased solution P concentrations increased growth and shoot P concentrations in both leeks and peppers, but decreased the degree of mycorrhizal infection of the root systems. At low solution P concentrations, inoculation increased the shoot P concentrations and growth of the peppers, but decreased the shoot P concentrations of the leeks. Increasing the number of spores per plant did not influence growth or tissue P concentrations of transplants, but did increase mycorrhizal infection at low and intermediate solution P concentrations.
Abstract
Transplants of ‘Healani’ tomato (Lycopersicon esculentum Mill.) and ‘Yellow Granex’ onion (Allium cepa L.) inoculated with the vesicular-arbuscular mycorrhizal fungus (VAMF) Glomus aggregatum (Schenck and Smith emend. Koske) were grown in peat-vermiculite fertilized with solutions containing 4, 16, 64, or 256 mg P/liter, applied daily or every 4 or 8 days. Increasing the total amount of P available to the transplants by either increasing the P concentration or by decreasing the interval between applications increased plant total fresh weights (TFW) and shoot P concentrations, but decreased root VAMF infection. Inoculation reduced tomato TFW when P availability was high. Inoculation increased onion shoot P concentrations and TFW only when P availability was very low. Frequent applications of solutions low in P produced larger transplants with higher levels of VAMF infection than did similar total amounts of P supplied less frequently but at higher concentrations. Different combinations of P concentration and application intervals were required for the production of vigorous mycorrhizal tomato and onion transplants.
Abstract
A sand medium containing activated alumina was developed to provide a range of stable, reproducible P concentrations in plant cultures. The lowest P levels compare favorably to concentrations found in soils. Activated alumina was “loaded” by absorption of phosphate from 0.01 m NaCl solutions containing KH2PO4. Phosphorus concentrations in solutions expressed from sand-alumina mixtures were dependent upon the P concentrations used to absorb P onto the alumina. Increasing the density of a specifically loaded alumina did not affect the average solution P concentration in the cultures but did result in substantial increases in total dry weight yields of tomato (Lycopersicon esculentum Mill.) plants grown in the cultures. Thus, diffusion of P to root surfaces seems to be a prominent limiting factor in this system as in soils. The sand alumina culture technique shows promise for simulating plant responses to P at concentrations and under conditions comparable to those found in soils.