Phytophthora capsici is a serious soilborne pathogen in chile pepper [Capsicum annuum L.] in New Mexico, and has been shown to spread under high soil moisture conditions and cause losses in a wide array of crops worldwide. This study was conducted to assess whether soil water saturation predisposes chile pepper to infection by P. capsici. Potted chile pepper plants of `Criollo de Morelos 334' (`CM334') and `New Mexico 6-4' (`NM6-4'), resistant and susceptible to P. capsici, respectively, were subjected to soil water saturation conditions (saturated and nonsaturated) for 3 and 6 days at two growth stages (six- to eight-leaf stage and one- to four-flower bud stage) prior to being inoculated or noninoculated with zoospores of P. capsici. Regardless of growth stage, no disease symptoms developed in `CM334' grown either under saturated or nonsaturated soil conditions at any of the two periods (3 or 6 days) of soil water saturation. In `NM6-4', disease symptoms consisting of stem necrosis, defoliation, and wilting were expressed. Plant growth stage at inoculation had a significant effect on disease severity (P < 0.0001). However, the response of `NM6-4' to P. capsici at each growth stage under saturated soil conditions was similar to that under nonsaturated conditions regardless of the period of saturation (P = 0.09). These results indicate that soil water saturation does not exert a significant predispositional effect on infection of chile pepper by P. capsici.
H. Melakeberhan, G.W. Bird, and A.L. Jones
This study was conducted as part of a stone fruit decline project to determine the effects of soil pH (3.9 to 7.0) on soil and plant nutrient imbalance and mortality of standard (Mazzard and Maheleb) and new (GI148-1 and GI148-8) rootstocks. Seedling mortality and soil Ca in all rootstocks and soil K and leaf Ca, K, Al, and Mn contents in all rootstocks but GI148-8 were higher at below optimum than at optimum soil pH. The nutrient imbalance suggests that the adaptation of these rootstocks to biotic and abiotic factors needs to be considered.
J.L. Lyles, J.D. MacDonald, and D.W. Burger
Roots of hydroponically grown Hibiscus Rosa-sinesis L. cuttings were exposed to 22, 30, 40, or 50C for 20 minutes, after which they were inoculated with zoospores of Phytophthora parasitica Dastur. Visual assessment of root discoloration and culturing of randomly selected root pieces 10 to 13 days after treatment showed that roots exposed to 40 or 50C had a significantly higher incidence of infection than those exposed to 20 or 30C. Plants were also grown in pots containing University of California (UC) mix or washed, graded sand and exposed to solar radiation for 1 day or 3 weeks, respectively. Root systems of plants in direct sunlight heated to 52C, while roots of shaded plants heated to 40C. Assessment of infection severity was done visually or by means of a Phytophthora-specific antibody probe. In all experiments, infection severity was highest in sun-exposed plants and was insignificant to moderate in shaded plants.
T.J. Swiecki and J.D. MacDonald
Exposure of tomato plants (Lycopersicon esculentum Mill.) to salinity stress either before or after inoculation with Phytophthora parasitica increased root and crown rot severity relative to nonstressed controls. The synergy between salinity and P. parasitic was most pronounced on young (prebloom) plants and least pronounced on older (postbloom) plants. Salt stressed, inoculated plants had significantly reduced top weight, significantly more root necrosis, greater incidence of crown necrosis, and significantly greater mortality. Increased disease severity occurred even though experiments showed salinity reduced zoospore release arid motility of P. parasitic, suggesting that even low inoculum levels can result in severe root rot on young tomato plants in saline soils.
Todd W. Wert, Jeffrey G. Williamson, Jose X. Chaparro, E. Paul Miller, and Robert E. Rouse
. Testing of different cultivars at multiple locations can help to determine their range of adaptation. The prevalence for the increased proportion of blind nodes can be cultivar-specific and some genotypes have a predisposition for this trait. Our results
Joyce G. Latimer
Since chemical growth retardants are no longer labelled for use on vegetable transplants, mechanical conditioning provides an alternative method of controlling excessive stem elongation under greenhouse conditions. Mechanical conditioning includes brushing or shaking treatments that physically impact or displace the plant and generally reduce plant growth, increase stem and petiole strength, and improve overall plant quality. The resulting transplants have less breakage during postharvest handling, may be more stress tolerant, and are faster to establish in the field. However, only minor effects on crop yield have been identified. Brushing reduced broccoli transplant size, but improved shoot dry weight gain during field establishment but had no effect on head yield. Brushing is a labor intensive practice for large-scale operations. Current attempts to mechanize brushing require that the plants are uniform in height and treatment tolerant. Additional research in non-contact treatments like shaking or vibration of benches is necessary. The effects of the treatments on stress tolerance and predisposition to disease need to be clarified.
Akhtar Ali and James R. Baggett
The inheritance in corn (Zea mays L.) of resistance to head smut disease incited by Sphacelotheca reiliana (Kuhn) Clinton was studied in the field on crosses of resistant dent corn line N6 with two susceptible sweet corn (su1) inbred lines. Disease incidence in the resistant parent (Pr) was 0% to 4%, and 83% to 96% in the susceptible parent (Ps). Predisposition of seedlings by clipping just above ground level increased percent infected in progeny populations by as much as 4-fold, but did not affect disease incidence in the, parents. At the lower disease incidence of unclipped plots, the F1, F2, and BCr means were close to the mean of Pr, suggesting dominance of resistance. At the high disease incidence of clipped plots, the relationship of parent and progeny means “suggested additive inheritance. Epistasis was also generally present with a higher level indicated for unclipped plots. Inheritance was concluded to be quantitative. Reciprocal differences were observed only in backcrosses. In the F2 and BCs populations, plants grown from dent (Su1) seed were lower in disease incidence than plants grown from su1 seed.
Michael A. Schnelle
Four ornamental species, lyreleaf salvia (Salvia lyrata), roughleaf dogwood (Cornus drummondii), northern sea oats (Chasmanthium latifolium), and cholla (Cylindropuntia imbricata), are all native to Oklahoma and nearby states. They all possess ornamental attributes and range from widespread to niche crops in the nursery industry and are also cultivated for their utilitarian, herbal, and miscellaneous merits. Their allure to customers and their ability to thrive in a myriad of environments is a major impetus for commercial growers and retailers to carry these species. However, their extraordinary ability to adapt to a plethora of environmental conditions, in the built environment or in their native range, also enables them to often outcompete neighboring flora. Their predisposition to be opportunistic, and ability to grow in challenging locations, sometimes results in their becoming a nuisance or even invasive (i.e., capable of displacing other native flora or fauna). Plants featured are described for their marketable attributes but also reviewed for control measures (e.g., herbicides, prescribed burning, improved grazing practices) when they grow in an aggressive manner.
Svoboda V. Pennisi, Dennis B. McConnell, and Michael E. Kane
We induced preferential allocation of Ca to two calcium oxalate (CO) sinks in immature leaf tissues of D. sanderiana: subepidermal extracellular deposits and intracellular raphides. Allocation was affected by exogenous Ca levels. Two groups of rooted cuttings were termed Ca-deficient and non-deficient. The first group consisted of cuttings that had been deprived of Ca for 18 months, and, the second, cuttings rooted under standard horticultural conditions. All plants were grown in liquid medium supplemented with 100 ppm of potassium nitrate and subjected to 0, 3, or 7mm Ca from calcium acetate. The most striking feature of Ca-deficient plants grown in 0 mm Ca was the absence of intracellular raphides in the leaf primordia. The largest number of intracellular raphides developed in Ca-deficient plants grown in 7 mm Ca. The number of extracellular crystals in Ca-deficient plants grown in Ca-supplemented solutions versus non-supplemented were similar, but crystals were considerably smaller in non-supplemented plants. Total number of extracellular crystals per epidermal cell did not differ significantly between plants in all treatments. This implies that nucleation sites are pre-determined and finite in number. In contrast, the number of intracellular raphides was highly variable. In terms of Ca prioritization, the extracellular crystals took precedence over intracellular raphides, and this was most obvious in Ca-deficient plants. The significance of this research is that the extracellular crystals represent Ca sinks with limited induction capacity compared to intracellular Ca sinks. Plants with genetic predisposition for intracellular CO crystal formation may be able to respond favorably to root environments with low Ca levels compared to species with limited capacity for intracellular CO deposition. Intracellular CO crystals, therefore, play an integral role in plant nutrition as Ca storage sinks.
cooling of harvested strawberries has long been associated with maintaining optimal fruit quality during handling. However, delays of several hours between harvest and cooling often occur. Nunes et al. (p. 153 ) made an assumption that predisposition to