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Graduation date: 1994

Distribution of Fusarium wilt of muskmelon and watermelon in southwestern Ontario was studied. Particular attention was paid to morphological and physiological variations of the isolates obtained. Morphological variations were based on comparison in culture with a selected standard. Physiological variations were detected by pathogenicity experiments, and a study of assimilation of various carbon and nitrogen compounds. Some further aspects of the biology of the organisms were investigated. An experiment was carried out, employing several muskmelons and watermelon varieties, to compare their resistance under field conditions. / Thesis / Master of Science (MS)

Muskmelon (<i>Cucumis melo</i> L.) embryos are surrounded by a single layer of endosperm and a two- to four-cell-layered perisperm. The embryonic axis must penetrate the perisperm envelope (perisperm + endosperm) for germination to occur. Radicle emergence could result from increased turgor, weakening of the perisperm tissue, or a combination of both. In a previous report, turgor of the embryonic axis did not increase prior to radicle emergence. This suggests that weakening of the perisperm envelope is a prerequisite for radicle emergence in muskmelon seeds. The changes in cell wall sugars of the perisperm tissue were studied during imbibition using gas chromatography and high performance thin layer chromatography. The major cell wall sugars identified in the micropylar perisperm tissue were glucose, galactose, xylose, and rhamnose. Endo-β-mannanase has been shown to be responsible for endosperm degradation in seeds of Solanaceae, Leguminosae, and Fabaceae. However, the lack of mannose in the cell walls of muskmelon perisperm tissue suggests that this enzyme is not involved in muskmelon seed germination. Structural changes of the micropylar perisperm envelope tissue were visualized during imbibition using electron microscopy. Scanning electron microscope images revealed changes in the perisperm envelope before radicle protrusion. The cell walls of the perisperm envelope tissue were degraded starting 5 h prior to radicle emergence. An Instron was used to measure the mechanical resistance of the perisperm envelope during imbibition. The force and total energy required to penetrate the perisperm tissue of imbibed muskmelon seeds decreased gradually during imbibition. This study confirmed that the perisperm envelope tissue offered mechanical resistance to the expanding embryonic axis. Degradation of the perisperm envelope tissue before radicle protrusion facilitated radicle emergence. / Master of Science

The stage of maturity of seeds at harvest is an important factor that determines seed vigor. Separating seeds from a seed lot composed of many different stages of development can be difficult especially after maximum dry mass is attained. Separating seeds based on their physiological maturity is more challenging than sorting seeds based on their physical properties. Seeds may be non-destructively sorted using chlorophyll fluorescence (CF) as a marker of seed maturity. This study was conducted to test whether CF could be used to remove low vigor immature seeds from muskmelon (Cucumis melo L.'Top Mark') and tomato (Lycopersicum esculentum) seed lots. Light treatments were applied to determine whether the light environment during seed harvesting and processing could affect chlorophyll content and seed vigor. Seeds from nine stages of development were collected from 'TopMark'. Seeds from three stages of fruit development (red ripe, breaker, and mature green) were harvested from tomato cultivar Money Maker and two phytochrome mutants: phytochrome A mutant, fri-1 and phytochrome B mutant, tri-1. The SeedMaster Analyzer (Satake USA Inc., Houston Texas) was used to measure CF and to sort individual seeds according to CF levels. Immature tomato seeds and muskmelon, harvested from green fruits, had the highest CF (p>0.001). Contrary to the results obtained with the other tomato genotypes, the vigor of tri-1 did not change inversely with changing CF levels, rather, seeds with low CF had the same vigor as seeds with high CF. This result may suggest that the presence of phytochrome B exerts an inhibitory influence on vigor in tomato seeds, and that the persistent presence of chlorophyll during seed development does not affect vigor. The light treatments had no consistent effect on seed chlorophyll content or on vigor in either tomato or muskmelon. / Master of Science

Call number: LD2668 .T4 1984 B425 / Master of Science

Chitinase has been suggested to play a role in defense mechanisms. In this study, the activity and expression of chitinase in muskmelon seeds were investigated. Multiple chitinase isoforms were detected in muskmelon seeds from early development through radicle emergence. One acidic and three basic chitinase isoforms were detected in developing seeds at 40 days after anthesis (DAA). Both acidic and basic chitinase isoforms were detected in endosperm tissue during seed imbibition and after radicle emergence. Basic chitinase isoforms, but not acidic isoforms, were detected in embryo tissue. Basic chitinase isoforms were also detected in the embryonic axis or radicle tissue. Taken together, these observations indicate that chitinases are regulated developmentally and in a tissue-specific manner in muskmelon seeds. Therefore the potential function of chitinases in muskmelon seeds is discussed. Two complete cDNAs, Cmchi1 and Cmchi2, and a partial genomic clone of Cmchi2 have been isolated from muskmelon seeds. Cmchi2 gene has two introns in the coding region while Cmchi1 is intronless. Cmchi1 cDNA encodes a class III chitinase while Cmchi2 cDNA encodes a class II chitinase. Cmchi1 and Cmchi2 proteins might be targeted to secretory pathways because they possess signal peptides. Southern blotting suggested that there is at least one additional gene similar to Cmchi1 in the muskmelon seed genome, while there is only one copy of Cmchi2. Northern blotting analysis showed that both Cmchi1 and Cmchi2 are expressed in the radicle tissue at the time of radicle emergence. This indicates that the expression is regulated developmentally and in a tissue-specific manner. Salicylic acid (SA) and benzothiadiazole (BTH) stimulated the expression of Cmchi1 but not Cmchi2 in seeds after radicle emergence, indicating that SA might be involved in inducing the expression of Cmchi1, while a different signal might be involved in triggering the expression of Cmchi2. The protein encoded by Cmchi1cDNA was expressed in E.coli. It did not show any enzymatic activity. Western blotting using an antibody raised against the class III chitinase protein in cucumber was inconclusive, as this antibody recognized the purified Cmchi1 fusion protein and other unknown proteins isolated from the embryonic axis or the radicle tissue. / Ph. D.

An experiment was instituted to incorporate resistance to the powdery mildew fungus <i>Erysiphe cichoracearum</i> DC into the Ambrosia muskmelon, a melon of the Casaba or winter type. First generation hybrid (F1), first generation backcross (B1) and second generation inbred (F2) plants were grown to maturity at Blacksburg and Warsaw, Virginia. On the basis of the data obtained the following conclusions are drawn: • The muskmelon material acquired from the Plant Exploration and Introduction Service is a good source of powdery mildew resistance and of the material tested, PI3 showed the most promise as a source of commercial resistance. • The general technique of hybridizing a susceptible with a resistant plant can be used to advantage in incorporating disease resistance into the Ambrosia melon. • Further work is needed to obtain a commercially acceptable Ambrosia melon which is essentially homozygous for resistance to powdery mildew, and to determine the exact mechanism of inheritance of powdery mildew resistance. / Master of Science

Field experiments were undertaken to predict the yield of 'Earligold' muskmelon grown with plastic mulches, rowcovers and thermal water tubes. Mulches were either black, photoselective or clear. Rowcover systems included a clear perforated polyethylene, a polypropylene agrotextile, or unperforated polyethylenes (standard or infra-red treated) with a water-filled tube. In all tunnel types, the photoselective mulch had an intermediate effect between clear and black mulch on air and soil temperatures, chilling injury and days to flowering. Plants with a clear mulch and an infrared or standard unperforated tunnel with a thermal tube survived chilling temperatures between 1.6-5.8C for seven days, flowered first, had the heaviest biomass at anthesis and had the highest early yields. Plant dry weight from transplanting to anthesis was predicted from a multiple linear regression based on heat unit formulas using air (base temperature of 14C, maximum threshold of 40C) and soil temperatures (base temperature of 12C). The base temperature for predicting developmental time to anthesis of perfect flowers was 6.8C. In order to study fruit growth, a rapid and non-destructive method for estimating volume of ovaries was established. Fruit phenology was described as six classes for flower development and seven for fruit development. Flower abortion was studied in relation to each class. Plants displayed either one or two fruit growth cycles. The second cycle was triggered as the absolute growth rate of the first cycle fruits decreased. Developmental time of individual fruits was predicted from a heat unit formula with a base temperature of 15C when temperatures were recorded from a meteorological station. Another heat unit formula was proposed for air temperature at 7.5 cm. Fruit growth from the second cycle had a 60-degree day lag. Fruit volume proportion from blooming to maturity of first cycle fruits was described by a common Richards function. Although 65% of the plants produc

Experiments were conducted in 1997, 1998 and 1999 to determine the effects of mulch/mini-tunnel and thermal-water tube combinations on daily carbon dioxide (CO2) concentration, air, soil temperatures and early growth of muskmelons (var. Earligold) during the vegetative phase. Treatments consisted of mulched plot covered with a clear perforated, a clear non-perforated or a non-perforated infrared polyethylene mini-tunnel with the absence or the presence of a thermal-water tube compared with control treatments. Additional treatments consisting of the ventilation non-perforated clear and infrared tunnels containing no tube were used in 1998 and 1999. The non-perforated tunnels significantly increased CO2 concentrations, air and soil temperatures compared with those of perforated tunnels and controls. Inclusion of a thermal-water tube reduced air temperature fluctuations in the tunnels. Ventilating the non-perforated tunnels significantly decreased CO2 concentrations and air temperatures. / During the first 10--15 days after transplanting, muskmelons grown in the non-perforated tunnels had higher relative growth rate (RGR), net assimilation rate (NAR), and dry weight than those of grown under perforated tunnels and in the control plots. However, during the later period, 11--16 days after transplanting to anthesis, the effects of mulch/mini-tunnels on the RGR, NAR and dry weight of muskmelons were inconsistent. Muskmelons grown in the mulch/tunnels had significantly higher RGR, but generally lower NAR, than those of grown without tunnel. The use of mulch/mini-tunnels significantly increased dry weight at anthesis in 1997, but not in 1998 and 1999. The presence of thermal-water tube in the tunnels and ventilating the non-perforated tunnels generally increased RGR, NAR, and dry weight of muskmelons. The use of mulch/mini-tunnels reduced time for muskmelon to reach anthesis by 9 to 11 days. / The leaves of muskmelons grown in mulch/mini-tunnels had significantly lower ratios of variable to maximum fluorescence (Fv/Fm) than control plants throughout the experiments, except at 10 and 20 days after transplanting in 1997. Leaves of muskmelons grown in non-perforated tunnels had significantly higher levels of chlorophyll than all other treatments during first 15 days after transplanting. However, chlorophyll values in these treatments decreased as muskmelons reached anthesis. The presence of a thermal-water tube in the mulch/mini-tunnels and ventilating the non-perforated tunnels generally increased both Fv/Fm ratios and chlorophyll levels of muskmelon leaves.