Cucurbit Genetics Cooperative Report 7:49-50 (article 22) 1984

Effect of Methodology on Expression of Intercultivar Differences in Response to NaCl Stress in Melons

H. Nerson, H.S. Paris, Z. Karchi, Y. Burger, and M. Edelstein

Department of Vegetable Crops, Agricultural Research Organization, Newe Ya'ar Experiment Station, P.O. Haifa, Israel

Most vegetable crops are sensitive or moderately sensitive to salinity (1). Melons are classified as moderately tolerant (3) and are a potential crop for irrigation with saline water (2).

Sources of salt tolerance within a crop must be identified as the first step in a breeding program whose goal is to develop cultivars having higher salt tolerance. Several methods of screening and selection for salt tolerance have been evaluated for many crops (4).

Our objective was to compare responses of four melon accessions from diverse genetic backgrounds to salinity stress induced by three screening methods, and to relate these results to field test results. Accessions compared were the Israeli muskmelon 'Galia', the Israeli casaba 'Noy 'Amid', the European casaba 'Rochet', and a muskmelon introduction from Iran designated "Persia 202". The three screening methods were: (a) Seedlings were grown in 250 ml pots filled with fine gravel which were put in slightly larger pots containing Hoagland solution. At the first leaf stage (about ten days after emergence), NaCl at the rate of 10,000 ppm was added to the nutrient solution, which was renewed every other day. The pots were placed in growth chambers at two temperature regimes (day/night), 31C/23C and 23C/15C, with a 12-hour photoperiod. (b) Similar to a except that the pots were filled with a 4:1 (by volume) mixture of local silty loam:vermiculite at two salinity levels, 10,000 and 15,000 ppm, and (c) Seedlings were grown in larger pots (600 ml), in the greenhouse, with the same mixture as in b. NaCl at 15,000 ppm was introduced at the same developmental stage as in a and b but by daily application of 50 cc/pot in the nutrient solution.

Fourteen days after the beginning of salinization, plants were analyzed for growth, the data being presented in Table 1. Comparison of control results among the various methods revealed three different levels of seedling growth. The most favorable conditions were in c (larger pot, fertile medium, and high radiation) while the poorest were in a (small pot, hydroponic, inert medium, and relatively low radiation). Differences among accessions in response to NaCl stress were inconsistent among the three methods. For a given method, the most clear-cut difference occurred in c, where 'Rochet' was far superior to the other accessions tested.

Table 1. Effect of three methods of NaCl application on absolute growth (mg dry weight) and relative growth (% of control) of four melon accessions, 14 days after salinity introduction.
Accession	Salinity level (ppm NaCl)	Methodz
		a		b		c
		mg	%	mg	%	mg	%
Galia	0	203		437		1110
	10,000	148	73 a	274	63ab
	15,000			252	58 b	400	36 b
Noy 'Amid	0	201		555		1149
	10,000	123	61 ab	380	68 ab
	15,000			321	58 b	454	39 b
Persia 202	0	231		469		991
	10,000	129	56 b	340	72 a
	15,000			285	61 ab	368	37 b
Rochet	0	276		512		1109
	10,000	162	59 ab	316	62 ab
	15,000			304	59 b	695	63 a
zAverage of temperature regimes (see text). Mean separation in relative growth (%) columns by Duncan's multiple range test, 5% level.

The two casabas, 'Rochet' and 'Noy Amid', were compared in a field experiment for sensitivity to salinity. Expressed in terms of percent yield reduction, 'Rochet' was less sensitive to salinity than 'Noy 'Amid', consistent with the performance of these two cultivars in method c. This suggests that screening for salt tolerance should be conducted under as near to optimal growing conditions as possible. Such conditions would reduce confounding effects of various other environmental stresses and enable each accession tested to express its full salt-tolerance potential.

Literature Cited

1. Maas, E.V. and G.J. Hoffman. 1977. Crop salt tolerance--current assessment. J. Irrig. Drain. Div., Amer. Soc. Civil Engin. 103:(1R2)115-134.
2. Pasternak, D., I. Borovic, Y. De-Malach, and A. Davidson. 1980. Production of melons in the Negev Highlands with brackish water for summer and early autumn export. Hassadeh 61:133-138 (in Hebrew with English abstract).
3. Shannon, M.C. and L.E. Francois. 1978. Salt tolerance of three muskmelon cultivars. J. Amer. Soc. Hort. Sci. 103:127-130.
4. Shannon, M.C. 1979. In quest of rapid screening techniques for plant salt tolerance. HortScience 14:587-589.

Contribution No. 980-E, 1983 series, from the Agricultural Research Organization, Bet Dagan, Israel.