Search Results

You are looking at 1 - 4 of 4 items for

  • Author or Editor: D.H. Willits x
  • Refine by Access: All x
Clear All Modify Search
Free access

M.M. Peet and D.H. Willits

Excess irrigation water was provided to spring crops of bag-grown greenhouse tomatoes (Lycopersicon esculentum Mill.) to test the effect on radial fruit cracking. Varied numbers of emitters were placed in bags filled with soilless medium to provide different amounts of irrigation water. In 1990, all emitters provided water containing nutrient solution, but in 1992, the extra water added in one treatment did not contain nutrient solution. In both years, the percentage of cracked fruit was 20 percentage points higher in the treatments receiving more water. The increase in cracking was similar whether or not nutrient solution was added to the extra water. There also were some effects of the extra water on yield. Fruit count per plant was slightly higher (9.5%) when extra water was provided without nutrient solution, but was the same when nutrient solution was added to the extra water. Fruit weights per plant were 18.6% higher in 1990 when watering was increased. In 1992, fruit weights were similar, except for the treatment where the extra water provided did not contain nutrient solution. Fruit weight in this treatment was 19.7% higher than in the other treatments. In both crops, the percentage of cracking increased as linear and quadratic functions of cluster positions, i.e., there was more cracking in the upper clusters. In greenhouse situations, growers should consider water reduction when experiencing high levels of fruit cracking and as a precautionary measure when harvesting from the upper clusters. Providing excess water to greenhouse-grown tomatoes may be a viable technique for screening cultivars or for conducting research on practices to reduce cracking.

Free access

D.H. Willits and M.M. Peet

Chlorophyll fluorescence was measured under both laboratory and greenhouse conditions in an effort to develop a quick, reliable, and inexpensive laboratory procedure capable of predicting heat stress experienced by tomato (Lycopersicon esculentum Mill.) under greenhouse conditions. The laboratory tests consisted of measurements of the ratio of variable to maximal chlorophyll fluorescence (Fv/Fm) performed on leaf discs taken from whole tomato leaves and placed on a temperature controlled plate. Comparisons were made with greenhouse measurements of the same parameter conducted on intact leaves of whole plants exposed to different temperature treatments imposed by manipulation of the aerial environment of the greenhouse. Dark adaption periods ranging from 15 min to all day in the greenhouse and temperature exposure periods ranging from 5 min to 60 min in the laboratory were compared to find the best correlation between the two tests. Best agreement was obtained with 60 min treatment times in the laboratory and 60 min dark adaption periods in the greenhouse. Fv/Fm decreased quadratically with increasing leaf temperature in a similar fashion in both tests, suggesting that the laboratory approach can adequately predict plant response to greenhouse heat stress.

Free access

K.E. Tripp, M.M. Peet, D.H. Willits, and D.M. Pharr

Two cultivars of greenhouse tomato (Lycopersicon esculentum Mill.) were grown with ambient or 1000 μl CO2/liter during Jan.-June 1987 and 1988. In both years, CO2-enrichment increased foliar deformation and foliar starch, but during the season, foliar starch levels decreased while deformation increased. `Laura' had more deformation, while `Michigan-Ohio' had higher foliar starch concentration. During an entire season, there was no significant relationship between foliar starch concentration and deformation severity. Foliar C exchange rates in the lower canopy were not affected by severity of deformation. Data from these experiments do not support the hypothesis that excess foliar starch is responsible for foliar deformation at elevated CO2.

Free access

D.H. Willits, P.V. Nelson, M.M. Peet, M.A. Depa, and J.S. Kuehny

The results of six experiments conducted over 3 years were analyzed to develop a relationship between nutrient uptake rate and growth rate in hydroponically grown Dendranthema ×grandiflorum (Ramat.) Kitamura, cv. Fiesta. Plants subjected to two levels of CO, and three levels of irradiance in four greenhouses were periodically analyzed for growth and the internal concentration of 11 mineral elements. The resulting data were used to determine relative accumulation rate and relative growth rate, which were included in linear regression analyses to determine the dependence of uptake on growth. The regression equations were significant, with a slight trend toward nonlinearity in some elements. This nonlinearity seems to be related to the aging of the plant and suggests a process in the plant capable of controlling uptake rate, perhaps as a result of changes in the rate of formation of different types of tissues.