Cold Germinability of Cucumis melo

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Cucurbit Genetics Cooperative Report 8:41-43 (Article 16) 1985

Hutton, Mark G. and J. Brent Loy
University of New Hampshire, Durham, NH 03824 U.S.A.

Low soil temperatures in the early portion of the growing season, can severely limit muskmelon seed germination and early seedling development. In fact, low soil temperatures can often kill young seedlings. Our first step in a program to improve cold tolerance of muskmelon is the identification of cold tolerant germplasm.

Reported here are the results of low temperature germination tests of commercial cultivars and plant introductions obtained from the Regional Plant Introduction Station in Georgia. The following observations were made during germination tests: 1) mean number of hours until radical emergence, hypocotyl elongation, and cotyledon expansion, and 2) development of root hairs and lateral roots.

Two replications of ten seeds each were germinated at 30° and 15°C. The following observations were made at 48 hour intervals over a period of 96 hours for the warm treatment and 336 hours for the cold treatment: A) radical emergence longer than 1 mm, B) hypocotyl elongation beyond the peg, C) cotyledon expansion beyond the seed coat, D) root hair development, 0-4 scale, and E) lateral root development, 0-4 scale. Indices for mean hours to emergence, hypocotyl elongation, and cotyledon expansion were computed using the formula (Loy, 1979):

Index = S1T1+S2T+S3T3+ … SnTn
S1+S2+S3+ … Sn

where “S” equals the number of seeds showing the trait of interest and “T” equals the time in hours.

The lines were grouped into three classes on the basis of emergence indices: ‘cold tolerant’ (> 231 hours), ‘moderate cold tolerant’ (231-291 hours), and ‘cold sensitive’ (< 291 hours or no response) (Table 1). In most cases, although not all, lines exhibiting early radical emergence also developed faster with respect to hypocotyl elongation and cotyledon expansion.

In Fall of 1983, initial selections were made and planted in the glasshouse. Since making the initial selections, lines have been identified which appear more cold tolerant. These plants were self-pollinated, the seed harvested, and then tested as previously explained. Comparison of the emergence indices of the initial screening and the S1 generation suggests that the response is stable since the indices of the six lines examined were nearly identical, with the exception of NH53-1-4 (Table 2).

Table 1. Representative classes of cold tolerant, moderately cold tolerant, and cold sensitive C. melo cultivars.

zRating 0-4: Root Hair, Lateral Root. Scale: O – not present, 1 -present on a few roots, 2 – present on 0.5 of the roots, 3 -well developed on >0.5 of the roots, 4 – extremely well developed on &Mac179;0.75 of the roots.

Cv

Index

Developmental Ratingz

or

P.I.#

code#

15°C

%germ.

emer.

hyp.

cot.

192hr

240hr

288hr

336hr
Cold Tolerant
126190 159 75 221.2 250.2 273.6 1,0 1,1 2,2 2,3
126197 161 100 217.7 241.5 253.1 4,0 4,2 4,4 4,4
126200 162 100 218.7 243.1 279.2 0,1 0,1 0,2 1,3
126202 163 90 215.5 243.6 256.6 3,1 3,2 2,3 3,4
127575 183 80 230.7 254.5 270.7 4,1 4,2 4,3 4,4
140762 224 95 216.0 237.0 261.8 2,1 2,2 2,2 3,4
Moderately Cold Tolerant
136197 202 70 252.8 273.2 288.0 0,0 1,0 2,1 2,1
194052 397 70 251.7 298.4 332.6 0,0 0,0 0,1 0,1
201581 413 70 251.1 287.6 322.0 1,0 3,0 3,0 3,0
Pers. 202 450 100 240.0 264.0 285.6 1,0 1,0 0,1 2,1
Cold Sensitive
182937 350 35 304.0 336.0 336.0 0,0 0,0 0,0 1,0
211955 442 15 316.0 0.0 0.0 0,0 0,0 0,0 0,0
Del. 51 200 0 0.0 0.0 0.0 0,0 0,0 0,0 0,0

The data in Table 1 suggests that early radicle emergence may not indicate cold tolerance during later stages of seedling development. The accession “Persia 202” a reported cold tolerant line (Nerson et al. 1982) seems to support this idea. Additionally, it appears there are lines available which may be more cold tolerant than “Persia 202”.

The results of this initial study have shown that there seems to be enough diversity in the low temperature germinability and early seedling development to warrant additional study. Areas for future investigating are the inheritance of cold tolerance, the evaluation of how reliable petri dish germination tests are when compared to germination tests conducted in soil, and the relationship between cold tolerant germination and later seedling development.

Literature Cited

  1. Loy, J. B. and K. B. Evenson. 1979. Phytochrome regulation of seed
    germination in a dwarf strain of watermelon. J. Amer. Soc. Hort. Sci.
    104(4):496-499.
  2. Nerson, H., D. J. Cantliffe, H. S. Paris, and Z. Karchi. 1982. Low
    temperature germination of Birdsnest-type muskmelons. HortScience
    17(4):639-640.