USDA-ARS, 1636 East Alisal ST Salinas, CA 93905
Root-knot nematodes (Meloidogyne spp.) are responsible for marked reduction in crop production, such as tomato and sugarbeet, in many parts of the world. For this reason the understanding and the resources of resistance to root-know nematodes, if incorporated into suitable varieties, would be of considerable interest and value to breeders and growers. Resistance and inheritance of the resistance to root-know nematodes in tomatoes have been investigated for many years, e.g., Barham and Winstead (1957).
Four Meloidogyne species, which include seven races (Table 1) of root-not nematodes, were cultivated and preserved in the greenhouse. Due to an uncontrollable tobacco mosaic virus (TMV) infestation on tomato host variety 'Tropic", a virus-resistant line '74T-3' was adopted as the replacement. Unexpectedly, this tomato line furnished rather poor root-knot nematode reproductions after inoculation with sufficient eggs and larvae. In most cases, these inoculated plants formed either no visible galls or only very few tiny galls.
The culture of M. javanica was obtained from Dr. I.J. Thomason, U.C. Riverside. M. incognita race 1 was from Dr. B.B. Westerdahl, U.C. Davis. M. incognita races 3 and 4, M. arenaria races 1 and 2, and M. hapla were from Dr. K.R. Barker, N.C.S.U., Raleigh. Lycopersicon esculentum line 74T-3 was believed to have been obtained from Petoseed's years ago; its progenitor, however, is presently untraceable (Dr. Teresa B. Bunn, personal communication). Line 74T-3 has been maintained and selected at Salinas Station for resistance to TMV. Tropic was a susceptible tomato variety obtained from Dr. Thomason. LA 1610 was a L. pimpinellifolium accession originally from Dr. C.M. Rick, U.C. Davis. LA 2398 was a cu-3 dwarf curly leaf tomato mutant line derived from AL 1610 (Yu, 1989). LA 1610B was heterozygous for cu-3.
Table 1. Differential reproductivity of seven Meloidogyne species/races on specific Lycopersicon germplasm lines.
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Tomato Meloidogyne No. of Days Gall Size Total eggs
genotype species plants inocul. forma- mm and larvae
tion
Number
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74T-3 M. incognita-1 8 43 1.2 2.0 11
-3 8 43 1.8 1.4 173
-4 8 44 1.8 1.7 274
M. arenaria -1 4 48 3.6 1.6 441
-1p 8 42 1.3 1.3 298
-2 4 56 8.0 1.2 120
M. hapla 8 42 51.3 2.9 34620
M. javanica 8 42 3.8 1.5 199
Tropic M. incognita-1 6 43 205 4.3 61562
-3 6 43 59 2.9 61898
-4 6 42 181 2.8 42498
M. arenaria -1 5 55 59 3.1 27926
-1p 6 40 151 2.8 141881
-2 6 42 106 2.4 49874
M. hapla 6 40 50 2.2 53010
M. javanica 7 40 184 3.4 53750
LA 2398* M. incognita-1 2 40 28 2.0 16205
-3 2 41 67 2.0 20435
-4 2 41 67 1.5 19030
M. arenaria -1p 2 40 37 1.5 13055
-2 2 41 33 2.5 9329
M. hapla 2 41 15 1.1 8910
M. javanica 2 40 37 2.0 9362
LA 1610 M. incognita-3 6 43 50 2.5 19380
-4 6 42 114 2.1 37369
M. arenaria -1 6 45 43 2.2 17352
LA 1610B M. incognita-1 8 43 195 3.9 138713
M. arenaria -1p 8 43 129 4.2 172353
M. hapla 8 42 73 2.9 44928
M. javanica 8 42 142 3.2 134253
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* The dwarf curly leaf tomato plants were usually less vigorous than the
others.This study was conducted from February 6, 1991 to October 15, 1991 in the greenhouse. Seedlings were germinated in sand flats and transplanted individually to 200 ml cone-tainers having 1 soil: 9 sand mixture, maintained at 25 to 28 deg. C within wood frames. Plants were inoculated at the 5-7 leaf stage with 1500 to 2000 larvae per plant. Root systems of the inoculated plants were examined 40 + days after inoculations. All visible galls (regardless of sizes) and recoverable eggs and larvae were examine (Table 1). Obviously line 74T-3 was susceptible only to M. hapla, and resistant to all M. incognita, M. javanica and M. arenaria species and races. In the latter three groups, 33.3% (16 out of 48) of their inoculated plants were free from gall formation and nematode reproductions. Among the three groups, a mean number of 2.6 galls (2 mm size) were observed on the M. incognita race 1 inoculated 74T-3 roots, but no eggs or larvae were recovered. These results were in agreement to Barham and Winstead's observations. Thus line 74T-3 has carried either the Mi gene (Gilbert and McGuire, 1956) or an alike resistance factor to these three Meloidogyne species. The susceptibility of 74T-3 to M. hapla was similar to the rest of the test plants.
Literature cited:
Barham, W.S. and N.N. Winstead. 1957. Proc. Am. Soc. Hort. Sci. 69:372-377.
Gilbert, J.C. and D.C. McGuire. 1956. Proc. Am. Soc. Hort. Sci. 68:437-442.
Yu, M.H. 1989. Genome 32:359-364.