Date of Award
Program or Major
Doctor of Philosophy
J Brent Loy
Five hundred muskmelon accessions were evaluated for germinability at 15$\sp\circ$C and classified as cold germinable (CG) or non-cold germinable (NCG). Accessions meeting the following criteria were classified as CG: germination $>$80%, EI $\leq$ 240, HI $\leq$ 265, and CI $\leq$ 290. EI, HI, and CI are mean hours to emergence, hypocotyl elongation and cotyledon expansion respectively. Only 5% of the accessions examined were considered as CG.
Seedling growth of CG (PI 126156, PI 126197, and 'Persia 202') and NCG ('Delicious 51', 'Minnesota Midget', 'Old Time Tennessee', Russian 4141) muskmelon genotypes was compared. Seedlings were grown to 30$\sp\circ$C to the second leaf stage then transferred to either 15$\sp\circ$ or 30$\sp\circ$ treatment. Rate of leaf initiation over 16 days, leaf area ratio, specific leaf area, RGR (relative growth rate), dry matter partitioning and EI were determined. Leaf initiation rate and RGR most clearly separated differences between cold tolerant and sensitive genotypes. CG lines had the largest seed and plants at either temperature. EI was significantly negatively correlated with RGR and final plant size at 15$\sp\circ$. In contrast, EI was not correlated with RGR or plant size at 30$\sp\circ$.
A CG inbred derived from PI 126156 was crossed to a NCG inbred derived from 'Delicious 51' and an inbred developed from 'Minnesota Midget' with intermediate germinability at low temperature. Reciprocal F$\sb1$, F$\sb2$, and BC generation seed were germinated 14 days at 15$\sp\circ$C. Segregating data indicate in PI 126156 a cytoplasmic component (CG$\sb1$) that increases the capacity for cold germinability, a homorecessive gene conferring a high probability of germinability at 15$\sp\circ$ in the presence of CG$\sb1$, and one or two modifying genes which increase the probability and rate of germination.
In vitro pollen germination and growth of CG and NCG genotypes muskmelon were evaluated at low (13$\sp\circ$ or 15$\sp\circ$C) and high (30$\sp\circ$C) termperatures using hanging drop liquid cultures. Time of pollen collection greatly influenced pollen germination at low but not high temperatures. At low temperatures, CG lines had greater pollen germination than NCG lines. There were no significant differences in pollen tube lengths among CG and NCG lines.
Hutton, Mark Gordon, "Genetics and physiology of cold tolerance in muskmelon (Cucumis melo L)" (1988). Doctoral Dissertations. 1560.