Correlation of Shoot Weight with Root Galling in Cucumis spp. Inoculated with Root-knot Nematodes

admin

Cucurbit Genetics Cooperative Report 14:19-21 (article 8) 1991

Todd C. Wehner, S. Alan Walters and Kenneth R. Barker
Department of Horticultural Science (first and second authors) and Department of Plant Pathology (third author), North Carolina State University, Raleigh, NC 27695-7609

Root-knot nematodes (Meloidogyne spp.) are the most important pathogen of cucumbers (Cucumis sativus L.) in North Carolina. Root-knot nematodes destroy approximately 12% of the crop in the state annually (4). Root-knot nematodes reduce fresh weight of plants (i.e. plant stunting) as well as reducing plant yields (i.e. fruit production).

Methods. A greenhouse study was conducted to determine whether shoot weight and root galling were correlated in six Cucumis cultigens (C. sativus L. cv. Sumter and C. metuliferus Naud. PI 482448, PI 482450, PI 482452, PI 482454 and PI 482461). Root Galling was induced by inoculation of seedlings with one of four different species of root knot nematodes, M. hapla, M. arenaria race 1, M. incognita race 1, and M. javanica. The experiment was a factorial treatment arrangement in a randomized complete block design with four replications. Each treatment combinations consisted of one Cucumis cultigen and one root knot nematode species in a 100-mm diameter (1450 cm3 volume) pot. Pots contained sterilized sand and soil in a 1:1 ratio. Plants were grown from seed, with one plant per pot.

Inoculum was prepared using the technique developed by Hussey and Barker (3). Each pot was inoculated two weeks after planting with 5000 root-knot nematode eggs of the appropriate root-knot nematode species or race. Plants were rated after 10 weeks after planting for root-knot nematode damage (0 to 100% of roots galled), and shoot fresh weight.

Results. ‘Sumter’ had the lowest overall shoot weight and the highest percentage of galled roots, which indicated that it was the most susceptible cultigen tested (Table 1). However, ‘Sumter’ did not differ significantly from the other cultigens tested with respect to mean shoot weight. ‘Sumter’ was the most susceptible cultigen to M. incognita race 1, significantly different from the four plant introduction accessions of C. metuliferus (PI 482450, PI482452, PI482454 and PI 482461). With respect to mean percentage root galls, ‘Sumter’ was significantly different from the accessions of C. metuliferus tested. An accession of C. metuliferus, PI 482452, was the least susceptible cultigen tested, having a mean shoot weight of 514 g, and 35% of the roots galled.

Table 1. Shoot fresh weight (ShWt) and percentage of roots galled (%G) of ‘Sumter’ (C. sativus) and 5 accessions of C. metuliferus inoculated with 4 species of root-knot nematodes.z

Mean

Mh

Ma1

Mi1

Mj
Cultigen ShWt %G ShWt %G ShWt %G ShWt %G ShWt %G
PI 482452 514 35 529 6 448 36 484 50 596 46
PI 482454 499 42 552 6 588 40 420 60 434 60
PI 482450 469 43 552 6 367 60 448 66 510 41
PI 482461 478 50 546 16 493 56 417 80 456 46
PI 482448 413 56 398 20 445 50 381 86 428 66
Sumter 389 80 423 30 434 96 258 96 442 96
Mean 460 51 501 14 462 56 400 73 479 59
LSD (5%) for row-column comparisons of means 135 22

z Data are means of replications of 1 plant each. Shoot weight is in grams. Mh = M. hapla, Ma1 = M. arenaria race 1, Mi1= M. incognita race 1, and Mj = M. javanica.

Root galling was negatively correlated (-0.38) with shoot fresh weight (Table 2), as expected. Thus, susceptible plants with many root galls had a lower shoot weight than a resistant ones. Correlations were largest for plants inoculated with M. hapla or M incognita race 1, whereas plants inoculated with M. arenaria race 1 or M. javanica had only small negative correlations. The most pathogenic species tested was M. incognita race 1, indicated by the lowest shoot fresh weight and the highest percentage root galling (Table 1). The least pathogenic species tested was M. hapla.

Table 2. Correlations of fresh shoot weights and gall indices for each species of root-knot nematodes tested.z

Correlation

Overall

Mh

Ma1

Mi1

Mj
Shoot wt. vs. gall index -0.38 -0.64 -0.08 -0.58 -0.01

z Mh = M. hapla, Ma1 = M. arenaria race 1, Mi1= M. incognita race 1 and Mj = M. javanica.

These results confirm previous work showing that species of Cucumis are resistant to M. hapla (5, 6) and ‘Sumter’ (C. sativus) is more susceptible to root-knot nematodes than are accessions of C. metuliferus (1, 2). In addition, shoot fresh weight might be a useful trait to aid in the selection for nematode resistance.

Literature Cited

  1. Boukema, I. W., G. T. M. Reuling and K. Hofman. 1984. The reliability of a seedling test for resistance to root know nematode in cucurbits. Cucurbit Genetics Coop. Rpt. 7:92-93.
  2. Fassuliotis, G. 1967. Species of Cucumis resistant to the root-knot nematode, Meloidogyne incognita acrita. Plant Dis. Rptr. 51 (9):720-723.
  3. Hussey, R. S. and K. R. Barker. 1973. A comparison of methods of collecting inocula of Meloidogyne spp., including a new technique. Plant Dis. Rptr. 12: 1025-1028.
  4. Main, C. E. and S. K. Gurtz (eds.). 1989. 1988 estimates of crop losses in North Carolina due to plant diseases and nematodes. Dept. of Plant Path. Spec. Publ. No. 8, North Carolina State Univ., Raleigh, NC.
  5. Walters, S. A., T. C. Wehner and K. R. Barker. 1990. Resistance of the cucumber to the root-knot nematode, Meloidogyne hapla. Cucurbit Genetics Coop. Rpt. 13: 10-11.
  6. Winstead, N. N. and J. N. Sasser. 1956. Reaction of cucumber varieties to five root-knot nematodes (Meloidogyne spp.). Plant Dis. Rptr. 40(4): 272-275.