Radopholus arabocoffeae sp. n. (Nematoda ... - Donimabe.org.vn

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P.Q. Trinh et al. Fig. 4. Single unrooted tree constructed on basis of nucleic acid sequences using the maximum likelihood method. Table 2. Reproduction of Radopholus duriophilus and R. arabocoffeae sp. n. on carrot disks 50 days after inoculation with 25 females and incubation at different temperatures. Species Temp. Final population Rf ( ◦ C) Females Juveniles Males Eggs Total R. duriophilus 15 153 A* 33 A 29 A 19 A 234 A* 9.344 A* 20 964 B* 468 B* 128 B 1784 B 2748 B 109.92 B 25 10 212 D* 8984 D* 1524 C* 13 400 D* 34 120 D* 1364.8 D* 28 13 196 E* 18 196 E* 2936 C* 17 336 D* 51 664 E* 2066.56 E* 30 7008 C 5300 C 2348 C 7376 C* 22 032 C* 881.28 C* R. arabocoffeae sp. n. 15 127 a* 21 a 22 a 16 a 186 a* 7.44 a* 20 580 b* 776 b* 84 b 1908 b 2488 b 99.52 b 25 7408 d* 5596 d* 2828 c* 7376 d* 23 208 d* 928.32 d* 28 10 064 e* 12 064 e* 2816 c* 10 236 d* 35 180 e* 1407.2 e* 30 6308 c 4688 c 2244 c 5824 c* 19 064 c* 762.56 c* Data are averages of five replicates. Data were transformed to log 10 (x+1) before analysis of variance; untransformed data are presented. Per species, means in the column followed by the same letter do not differ significantly according to Duncan’s Multiple Range Test (P 0.05). Two populations were compared by T-Test: * indicates significant difference between R. duriophilus and R. arabocoffeae sp. n. per combination of stage and temperature (P 0.05). IDENTITY OF THE KRONG ANA RADOPHOLUS POPULATION In both morphology and morphometrics, the Radopholus population isolated from C. canephora in Krong Ana, Vietnam, almost completely matched the description of R. duriophilus (Nguyen et al., 2003). The only difference in morphology noted was in the stylet knob shape, which in the Radopholus population from C. canephora is directed anteriorly whereas in the type population of R. duriophilus the knobs are rounded, although sometimes with a dorsal projection. This difference is herein interpreted as intraspecific variation. MULTIPLICATION ON CARROT DISKS Both R. duriophilus and R. arabocoffeae sp. n. showed the lowest reproduction at 15 ◦ C; however, the high reproduction factor obtained for each of the species prove that 15 ◦ C is not the lower limit for their reproduction (Table 2). 690 Nematology
Radopholus arabocoffeae sp.n.fromVietnam Table 3. Reproduction of single females or single juveniles of Radopholus duriophilus and R. arabocoffeae sp. n. on carrot disks at 28 ◦ C. Population character Single female Single juvenile R. duriophilus R. arabocoffeae sp. n. R. duriophilus R. arabocoffeae sp. n. Number of juveniles/disk 4264 a 2832 b 139 0 Number of females/disk 4664 a 2172 b 166 0 Number of males/disk 1944 a 196 b 38 0 Females as % of total 29.2 a 23.2 b 30.9 0 Males as % of total 12.2 a 2.1 b 25.9 0 Juveniles as % of total 26.7 a 30.2 a 7.1 0 Eggs as % of total 31.9 a 44.5 b 36.1 0 Data are averages from five replicates. Data were transformed to log 10 (x + 1) before T-Test. Comparisons between single female inoculations of R. duriophilus and R. arabocoffeae sp. n. followed by the same letter are not significantly different (P 0.05). Both species reproduced in highest numbers at 28 ◦ C. At that temperature, the reproduction of R. duriophilus was higher than that of R. arabocoffeae sp. n. The optimum temperature of R. arabocoffeae sp. n. is similar to the optimum observed for R. similis (Holdeman, 1986; Fallas & Marban-Mendoza, 1994; Fallas & Sarah, 1995; Elbadri et al., 2001). Significant differences in multiplication between R. arabocoffeae sp.n.andR. duriophilus were also found at 15, 25, 28 and 30 ◦ C, although there was no significant difference at 20 ◦ C. These differences were significant for almost all developmental stages. At 28 ◦ C both Radopholus species reproduced easily from single females. Radopholus duriophilus had a higher reproductive fitness than R. arabocoffeae sp. n., whereas R. arabocoffeae sp. n. produced many more males (Table 3). When starting from single juveniles, only R. duriophilus reproduced. Reproduction of Radopholus species has been the subject of debate. Loos (1962), and Rivas and Roman (1985) reported that they did not obtain progeny from single R. similis juvenile inoculations and concluded that R. similis reproduced solely by amphimixis. Brooks and Perry (1962), however, showed that R. similis was able to develop up to three generations from a single egg inoculation and proposed that R. similis might reproduce via parthenogenesis. Kaplan and Opperman (2000) came to the conclusion that the rodshaped structures they observed in the spermatheca of R. similis females did not resemble sperm and did not result from mating, but were spermatids produced by the ovotestis of the hermaphrodite female. The authors concluded that hermaphroditism appears to afford the burrowing nematode with a reproductive strategy enabling individual nematodes to produce progeny without the assistance of males. Stanton et al. (2001) also observed rod- Table 4. Estimates of parameters of Seinhorst model of fresh weight (g) Coffea arabica cv. Catimor grown in 250 cm 3 pots after inoculation with three species of coffee nematodes. Nematode Plant part Parameter 1) R 2 species m T z y m y m · m Pratylenchus Total 0.50 0 0.8 4.864 2.432 0.94 coffeae Root 0.55 0 0.65 1.978 1.088 0.76 Shoot 0.45 0.18 0.85 2.886 1.299 0.94 Radopholus Total 0.25 0.8 0.75 4.864 1.216 0.94 duriophilus Root 0.20 0.5 0.70 1.978 0.396 0.93 Shoot 0.25 0.51 0.75 2.886 0.722 0.83 R. arabo- Total 0.10 0 0.70 4.864 0.486 0.96 coffeae Root 0.15 0.22 0.60 1.978 0.297 0.92 sp. n. Shoot 0.10 0 0.70 2.886 0.289 0.95 1) The Seinhorst model is of the form: Y = y m for Pi T ,and Y = y m · m + y m · z (P i−T) for Pi > T; y m = yield (g fresh weight) without nematode damage, m = a constant so that y m·m equals the minimum yield, z = parameter determining the slope of the curve, T = damage threshold density (nematodes per plant at inoculation). shaped structures in freshly moulted, apparently virgin, females of R. musicola and commented on the apparently hermaphroditic nature of this species. DAMAGE POTENTIAL The relationship between the initial densities of R. duriophilus, R. arabocoffeae sp.n.andP. coffeae and the weight of C. arabica cv. Catimor 90 days after inoculation fitted the Seinhorst model (R 2 > 0.76) Vol. 6(5), 2004 691
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