Cucurbit Genetics Cooperative Report 15:2830 (article 10) 1992
Use of Reproduction Factor and Gall Index in Determining Resistance in Cucumis spp.
Todd C. Wehner, S. Alan Walters and Kenneth R. Barker
Department of Horticultural Science, North Carolina State University, Raleigh, NC 276957609, Department of Plant Pathology, North Carolina State University, Raleigh, 27695
According to Taylor and Sasser (4), nematode reproduction can be used to measure rootknot nematode resistance, since reproductive ability on a given host is directly related to resistance. Oostenbrink's (2) reproduction factor (R = final nematode population/initial nematode population) is used to measure the reproductive capacity of nematodes. Ab Rfactor , 1 indicates an inefficient host (poor host); Rfactor . 1 indicates an efficient host (good host). Gall index measures plant damage (host response), whereas reproduction factor measure nematode reproduction (nematode response). Sasser et al. (3) proposed using a resistance rating system based on gall index (GI) and reproduction factor (R). We used a modification of this system for slightly resistant (R > 1) and GI , 40), and resistant R < 1 and GI , 40).
Methods. A greenhouse study was conducted to see how well reproduction factor (R = P_{f} / P_{i} ) along with gall index could determine resistance in species of Cucumis. One cultivar of C. sativus ('Sumter') and five accessions of C. metuliferus (PI 482448, PI 482452, PI 482454 and PI 482461) were inoculated with four different species of rootknot nematodes, M. hapla, M. arenaria race 1, M. incognita race 1, and M. javanica. In previous studies, African horned cucumber (Cucumis metuliferus Naud.) was resistant to rootknow nematodes, whereas cucumber (Cucumis sativus L.) was susceptible (6).
The experiment was a factorial treatment arrangement in a randomized complete block design with four replications. A treatment combination consisted of one Cucumis cultigen and one rootknot nematode species in a 100 mm diameter (1450 cm^{3} volume) pot. Pots contained sterilized sand and soil in a 1:1 ratio. Plants were grown from seed, each pot having one plant. Each plant was inoculated two weeks after planting with 5000 rootknot nematode eggs using the technique developed by Hussey and Barker (1). Plants were rated 8 weeks after inoculation (10 weeks after planting) first evaluating rootknot nematode damage using a gall index (0 to 100% of roots galled) and then measuring the numbers of eggs on roots. The number of eggs on the roots of each plant was determined using the technique for obtaining rootknot nematode eggs as described by Hussey and Barker (1).
Results. The number of juvenile nematodes in stage two (J2s) was not determined but Rfactor and gall index should be sufficient to determine resistance to these nematodes. Meloidogyne incognita race 1 was the most pathogenic species used, with an Rfactor and gall index mean of 5.3 and 73, respectively (Table 1). Furthermore, all but one cultigen had a susceptible rating when infected with M. incognita race 1 (Table 2). Five of six cultigens tested had Rfactors greater than four (an efficient host has an Rfactor > 1). Meloidogyne arenaria race 1 and M. javanica produced Rfactors over all cultigens of 2.6 and 3.3 respectively (Table 1), indicating that most cultigens evaluated were efficient hosts for those nematodes.
All cultigens evaluated were resistant to M. hapla based on Rfactor and Gall Index (Table 2). Resistance of C. sativus and C. metuliferus to M. hapla has previously been reported (5). Cucumis sativus 'Sumter' was the most susceptible cultigen tested with a mean Rfactor of 10.4, indicating that 'Sumter' was a good host for rootknot nematode reproduction. Of the C. metuliferus accessions, only PI 482452 had an Rfactor below one, indicating it was a poor host for rootknot nematode reproduction.
Of all rootknot nematodes evaluated, all plants were susceptible except PI 482452 (Table 2). Also, that accession was the only cultigen tested that was an inefficient host for M. incognita race 1. However, with respect to the rootknot nematodes evaluated, all C. metuliferus accessions tested were significantly different from C. sativus 'Sumter' except for M. hapla (Table 1). In this study, we found that Rfactor can be used to determine degree of resistance in species of Cucumis, since gall indies and Rfactors were somewhat comparable for each cultigennematode combination, which can be seen by the positive correlation (R = 0.68) between gall index and Rfactor.
Table 1. Reproduction factors (Rf) and gall indices (Gall) for 6 cultigens of Cucumis spp. infected with 4 species of rootknot nematode^{z}

Mean 
M. hapla 
M. arenarial 
M. incognita1 
M. javanica 
Cultigen 
Rf 
Gall 
Rf 
Gall 
Rf 
Gall 
Rf 
Gall 
Rf 
Gall 
Sumter** 
10.4 
80 
0.1 
30 
13.8 
96 
12.6 
96 
15.0 
96 
PI 482448+ 
1.7 
56 
0.0 
20 
0.7 
50 
4.5 
86 
1.4 
66 
PI 482461+ 
1.7 
50 
0.1 
16 
0.2 
56 
5.3 
80 
1.0 
46 
PI 482454+ 
1.6 
42 
0.0 
6 
0.4 
40 
4.5 
60 
1.3 
60 
PI 482450+ 
1.3 
43 
0.0 
6 
0.5 
60 
4.3 
66 
0.4 
40 
PI 482452+ 
0.3 
35 
0.0 
6 
0.1 
36 
0.5 
50 
0.7 
46 
Mean 
2.8 
51 
0.0 
14 
2.6 
56 
5.3 
73 
3.3 
59 
** Cultivar of Cucumis sativus
+ Accession of Cucumis metuliferus
^{z }Data are means of four replication of one plant each. Rfactor (R = P_{f} / P_{i}) is calculated as the average final count divided by 5000 eggs (initial number of eggs that pots were inoculated with). Gall index is the percentage of roots with galls (0 to 100 %) LSD (5%) for Rfactor = 3.8 and gall index = 22.
Table 2. Ratings of cultigens evaluated with rootknot nematodes.^{z}
Cultigen 
Mean 
M. hapla 
M. arenaria1 
M. incognita1 
M. javanica 
Sumter** 
S 
R 
S 
S 
S 
PI 482448+ 
S 
R 
MR 
S 
S 
PI 482461+ 
S 
R 
MR 
S 
MR 
PI 582454+ 
S 
R 
R 
S 
S 
PI 482450+ 
S 
R 
MR 
S 
R 
PI 482452+ 
R 
R 
R 
MR 
MR 
** Cultivar of Cucumis sativus.
+ Accession of Cucumis metuliferus.
^{z }Resistance ratings: susceptible (R > 1 and GI > 40), moderately resistant R < 1 and GI . 40), slightly resistant (R . 1 and GI < 40), and resistant (R < 1 and GI , 40). S = Susceptible, MR = moderately resistant and R = resistant.
Literature Cited
 Hussey, R.S. and K.R. Barker. 1973. A comparison of methods of collecting inocula of Meloidogyne spp., including a new technique. Plant Dios Rptr. 12: 10251028.
 Oostenbrink, M. 1966. Major characteristics of the relation between nematodes and plants. Meded. Landbouwhogesch. Wageeningen. 66: 146.
 Sasser, J.N., C.C. Carter and K.M. Hartman. 1984. Standardization of Host Suitability Studies and Reporting of Resistance to Rootknot Nematodes. North Carolina State University Graphics. Raleigh, NC 7 pp.
 Taylor, A.L. and J.N. Sasser. 1978. Biology, Identification and Control of RootKnot Nematodes (Meloidogyne spp.). N.C. State Univ. Dept. Plant Path., and USAID, Raleigh, N.C. 111 pp.
 Walters, S.A., T.C. Wehner and K.R. Barker. 1990. Resistance of the cucumber to the rootknot nematode, Meliodogyne hapla. Cucurbit Genet. Coop. Rpt. 13: 1011.
 Wehner, T.C., S.A. Walters and K.R. Barker. 1991. Resistance to rootknot nematode in cucumber and horned cucumber. Annals of Applied Nematology (Journal of Nematology 23, Supplement) 23(4S): 611614.