Use of cultivars resistant to high soil temperature could improve the performance of urban trees. The objective of this project was to examine selections of red maple (Acer rubrum L. and A. x freemanii E. Murray) for genotypic differences in resistance to root-zone heat stress. Development of roots and shoots from rooted single-node cuttings of seven genotypes grown in solution culture was optimal at about 28C. Shoot extension stopped within 3 weeks and terminal buds formed on plants of all genotypes at 36C. In a second experiment, the influence of 34C root-zone temperature on development varied significantly among six genotypes. Formation of terminal buds at 34C was observed only on plants of cv. Morgan and cv. Red Sunset. The reduction in new dry matter at 34C compared to plants at 28C ranged from 21% for cv. Schlesinger to 69% for cv. Morgan. We conclude that genotypes of red maple differ in resistance to high root-zone temperature.
Abstract
The response of ‘Red Delicious’ apples to low volume overtree evaporative cooling (EC) irrigation was studied over a 4-year period from 1969-72. While the amount of thermal load and irrigation system run-time varied from year to year, EC consistently resulted in fruit temperature reductions averaging 5.6°C (10.1°F) for the entire 509 hr the system operated over the 4-year period. In each of the 4 years, EC improved fruit quality; on the average increasing total reddish color 8%, solid red color 13%, soluble solids 1%, and fruit weight 22-g while reducing corking 8% and bitter pit 7%. The additional fruit coloration stimulated by EC concentrated harvest in the earlier portion of the harvest season. During the 4 years of the experiment, an additional 1/3 of the cooled crop was harvested, with sufficient solid red color to meet “extra fancy” U.S. grade, during the 1st 2 weeks of the seasons. Because of higher early-season prices, the concentrated earlier harvest of EC fruit is of considerable economic benefit. In locations where heat stresses are common, the use of EC and soil irrigation should be economically feasible.
Micropropagated `Red Norland' plants were transferred to an inert mixture of 1 perlite: 1 medium-grain quartzite (v/v) and grown 21 days at 20°C day/15°C night on a 25% Hoagland solution without Ca(NO3)2 (Ca at 10 mg·L–1 from CaCl2, N at 35 mg·L–1 from KNO3). Thereafter, Ca treatments (Ca at 0.2, 1, 5, 25, 125 mg·L–1) were imposed for 21 days with other nutrients unchanged. Day/night temperatures were 20/15°C and 35/20°C for control and stress plants, respectively. Continuous drip supply of nutrient solution in excess of demand maintained target rhizospheric Ca levels. All experiments were conducted in controlled-environment chambers with 400-μmol·m–2·s–1 light level. The following results were obtained. 1) Stress, but not control, plants grown with Ca at 0.2 and 1.0 mg·L–1 displayed reduced leaf expansion, extreme senescence, and death of the primary shoot meristem. 2) Plants grown with Ca at 5, 25 and 125 mg·L–1 grew normally under both temperature regimens, although plants responded to temperature with different biomass partitioning. (3) Total root mass at harvest was similar under all Ca–temperature combinations but low-Ca-treated plants had comparatively darker roots with fewer branches. (4) Light microscopic evaluation revealed normal staining patterns of lignified elements in leaves and stems of all plants. These data suggest that constant rhizospheric Ca levels >1 mg·L–1 are required for continued plant growth during exposure to heat stress.
Heat injury in creeping bentgrass (Agrostis stolonifera var. palustris Huds) has been associated with decreases in carbohydrate availability. Extending light duration may increase carbohydrate availability and thus improve growth of creeping bentgrass under heat stress. The objective of this study was to investigate whether turf performance and carbohydrate status could be improved by extending daily light duration for creeping bentgrass exposed to supraoptimal temperature conditions. `Penncross' plants were initially grown in growth chambers set at a day/night temperature of 20/15 °C and 14-hour photoperiod and then exposed to a day/night temperature of 33/28 °C (heat stress) and three different light durations: 14 (control), 18, and 22 hours (extended light duration) for 30 days. Turf quality and tiller density decreased with the duration of heat stress, as compared to the initial level at 20 °C, regardless of the light duration. However, both parameters increased with extended light duration from 14 to 18 or 22 hours. Extended light duration, particularly to 22 hours, also improved canopy net photosynthetic rate from -1.26 to 0.39 μmol·m-2·s-1 and daily total amount of carbon assimilation from -6.4 to 31.0 mmol·m-2·d-1, but reduced daily total amount of carbon loss or consumption to 50% through dark respiration compared to 14 hours treatment by the end of experiment. In addition, extending light duration from 14 to 22 hours increased water-soluble carbohydrate content in leaves both at the end of light duration and the dark period. These results demonstrated that extending light duration improved turf performance of creeping bentgrass under heat stress, as manifested by the increased tiller density and turf quality. This could be related to the increased carbohydrate production and accumulation. Supplemental lighting could be used to improve performance if creeping bentgrass is suffering from heat stress.
Abstract
An agrometeorological model was developed for assessing the effect of heat stress during flowering and early fruit set on avocado (Persea americana Mill) yields. This model accounted for heat stress only and was considered to occur when the daily maximum temperature was ≥33°C. In addition to the daily maximum temperature, the model considered the duration of such temperatures in days, as well as the timing of the occurrences of such temperatures in relation to the flowering and early fruit set of ‘Fuerte’ avocado. The specifications of the climatic data inputs are based on experimental results in the temperature range of 33° to 43°C extrapolated linearly. A series of weighting factors were used for the duration of heat spells in days. In the temperature range of 33° to 35° the weighting was n − 1; for the 36° to 38° range, 1.4n; and for the 39° to 43°C range, 2.0n. Weighting factors for the timing of the occurrence of heat spells follow closely the near-normal percentage distribution curve of open flowers. At bud burst in March, the weighting is 0.4, increasing to 1.3 at early fruit set by mid-May and decreasing rapidly to 0.3 by the end of June. The functional relationship between the model heat stress output and the yield of avocado for an irrigated, high-yielding plantation shows fairly good correlation, r 2 = 0.42 to 0.51, depending on the statistical method used. The agreement between the heat stress index and the yield of avocados is closely related only during those years when the plantation is subject to heat stress indexes greater than 10. Testing the model on independent data commenced in 1985 and includes a yield memory term.
Although heat stress injury is known to be associated with membrane dysfunctions, protein structural changes, and reactions of activated forms of oxygen, the underlying mechanisms involved are poorly understood. In this study, the relationships between thermotolerance and hydrogen peroxide (H2O2) defense systems, radical scavenging capacity [based on 1,1-diphenyl-2-picrylhydrazyl (DPPH) reduction], and protein aggregation were examined in vinca [Catharanthus roseus (L.) G. Don `Little Bright Eye'], a heat tolerant plant, and sweet pea (Lathyrus odoratus L. `Explorer Mix'), a heat susceptible plant. Vinca leaves were 5.5 °C more thermotolerant than sweet pea leaves based on electrolyte leakage analysis. Vinca leaf extracts were more resistant to protein aggregation at high temperatures than sweet pea leaf extracts, with precipitates forming at ≥40 °C in sweet pea and at ≥46 °C in vinca. Vinca leaves also had nearly three times greater DPPH radical scavenging capacity than sweet pea leaf extracts. Two enzymatic detoxifiers of H2O2, catalase (CAT) and ascorbate peroxidase (APOX), demonstrated greater activities in vinca leaves than in sweet pea leaves. In addition, CAT and APOX were more thermostable in vinca, compared with sweet pea leaves. However, tissue H2O2 levels did not differ between controls and tissues injured or killed by heat stress in either species, suggesting that H2O2 did not play a direct role in acute heat stress injury in vinca or sweet pea leaves. Greater thermotolerance in vinca, compared with sweet pea, was associated with greater DPPH radical scavenging capacity, indicating that AOS other than H2O2 may be involved in acute heat stress injury.
, which causes high input requirements when managing creeping bentgrass. Heat stress in summer months is a major problem for creeping bentgrass growing in temperate areas. There are many known physiological effects of heat stress on creeping bentgrass
Susceptibility of tomato (Lycopersicon esculentum Mill) genotpyes to the root-knot nematode Meloydogyne incognita and to heat stress can be evaluated in a single labor- and time-saving operation using a nondestructive in vitro excised root technique. Seeds are sterilized and germinated for 2 days on 1% water agar. Five-mm root sections are grown at 28 and 35 C for 30 days on Gamborg-B medium with and without nematode inoculum. Evaluation criteria include fresh and dry weight and the appearance of juveniles, adults, gulls, and egg masses. Evidence will be presented on the breakdown of resistance to M. incognita under high temperature stress.
Sublethal heat stress has been shown to decrease or eliminate deep supercooling of flower buds in woody plants and to release plants from endodormancy. Experiments were conducted to characterize the effect of heat stress on endodormancy and ecodormancy in peach (cv Loring) and two hybrid poplars. Protein synthesis (de novo) and patterns of protein expression were also monitored. In order to determine optimum treatment temperatures, shoots, collected September-March, were exposed to a range of temperatures (35-60 C) under wet or dry conditions for 1-6 h. Shoots were then placed in the greenhouse and cumulative budbreak was monitored over 4 weeks. Samples of bud and bark tissues were collected during and up to 72 h after heat treatment for SDS-PAGE analysis. Data indicate: 1) twigs must be immersed in water for the heat treatments to be effective; 2) heat treatments resulted in a release from endodormancy and a decrease in thermal units needed for budbreak during ecodormancy; 3) 40 C for 2-4 h was optimum in fall and late winter whereas 45 C was the optimum temperature to induce budbreak in midwinter; 4) optimum temperature for peach floral buds (37.5 C/2h) was lower than for vegetative buds (40 C/4h), and 5) heat treatments also decreased cold hardiness. Protein synthesis decreased significantly following heat treatment but was significantly greater than controls (room temp) 24-48 h after heat treatment.
Previously, we reported recovery of plants from “Near-Lethal” (NL) (Sub-Lethal) stresses was dependent on stage of development and post-stress environment Dormant plants exposed to NL-heat, freezing, and hydrogen cyanamide either died or were severely injured when stored at 0°C or recovered at 23°C and natural condition. This study reports on the changes in the evolution of metabolic heat in dormant red-osier dogwood (Cornus sericea L.) stem tissues after beat stress. Heat stress (51°C for half an hour) was followed by one of two post-stress environment (PSE) (0° or 23°C dark condition). Isothermal measurements of the heat of metabolism of the tissues were taken after 0, 1, 2, 5, 7 and 11 days of PSE. A significant reduction of metabolic heat generation occured in heat stressed plants at 0°C PSE from one to 11 days of incubation as compared to the non-stressed tissues. At 23°C PSE, no significant differences of heat generation between stressed and non stressed tissues were found within 7 days of incubation. The rate of metabolic. heat measured by decreasing temperature scanning microcalorimetry (21° to 1°C) were lower in beat stressed tissues. Arrhenius plots of metabolic heat rate gave a linear slope for non-stressed tissues and a complex slop for NL-stressed tissues at lower temperatures. Energy of activation (Ea) between 1°-8°C were 15.45 and 83.882 KJ mol-1 for NL-heat and non-stressed tissues, respectively.