Heritabilities for resistance to root knot nematodes (Meloidogyne javanica and Meloidogyne incognita races 1, 2, 3, and 4) were studied in a population of 226 sweetpotato clones of diverse origin. For each nematode isolate tested, 128-cell speedling trays were filled with previously inoculated substrate (30000 eggs/1000 mL substrate). Sweetpotato clones suitably tagged and identified were randomly planted in the cells (one plant/cell), with a total of four plants per clone per isolate. Ninety days after inoculation, sweetpotato plants had their roots washed for substrate removal, and treated with 150 mg·L–1 Phloxine B to stain nematode egg masses. The number of egg masses per root was recorded, and plants were accordingly assigned scores from 0 (highly resistant) to 5 (highly susceptible). Broad-sense heritability estimates were 0.87, 0.91, 0.81, 0.95, and 0.93 respectively for resistance to M. javanica and races 1, 2, 3, and 4 of M. incognita. The frequencies of resistant genotypes were higher for M. javanica and lower for M. incognita race 2. Genotypic correlations (rG) among the resistances to the various Meloidogyne isolates utilized were weak, ranging from 0.11 to 0.57, suggesting independent genetic controls. Clones could be selected, however, with high levels of resistance to all nematode isolates tested. (This work was supported by CNPq, CAPES, FAPEMIG, and FAEPE/UFLA.)
W. R. Maluf, S. M. Azevedo, and V.P. Campos
W.R. Maluf, L.V. Barbosa, and L. V. Costa Santa-CecÌlia
Oviposition and feeding of Scrobipalpuloides absoluta was studied on plants of seven different genotypes with varying 2-tridecanone (2-TD) foliage concentrations: Lycopersicon esculentum var. glabratum PI 1344417 (GLA), L. esculentum TSWV-547 (ESC), F1 (ESC × GLA), and four F2 genotypes—two with high 2-TD (HI1, HI2) and two with low foliage 2-TD concentrations (LO1, LO2). GLA, HI1, and HI2 showed 2-TD concentrations above 185 × 10–12 mol·cm2, while ESC, LO1 and LO2 had 2-TD below 40 × 10–12 mol·cm2; F1 had intermediary levels of 2-TD (83.5 × 10–12 mol 2-TD/cm2). Ovipositioning was substantially higher in the low 2-TD than on either the high 2-TD genotypes or in the F1, especially in the upper portion of the plants. Scores for leaf lesion type (LLT), overall plant damage (OPD) and percent leaflets attacked (PLA) were substantially higher for the low 2-TD than for either the high 2-TD genotypes or the F1. The results indicate that 2-TD mediates resistance to Scrobipalpuloides absoluta in the interspecific cross, and strongly suggest that 2-TD acts as both an ovipositioning and feeding deterrent for this insect.
José E.B.P. Pinto, Clovis M. Souza, and W.R. Maluf
Hybrid cabbage cultivars can be produced via seed-propagated self-incompatible (SI) inbred lines, or, alternatively, via vegetative propagation of SI clones. Cabbage clones differ in their ability to undergo vegetative propagation, a fact that appears to be related to the degree of differentiation of the axillary buds inside the head. A procedure for in vivo and in vitro propagation is described for cabbage clones known for difficulty in undergoing vegetative propagation. Cuttings from clonal families 800 (easy-to-propagate) and 007 (difficult to propagate) were immersed in indolebutyric acid (IBA—0, 5, 25, and 125 mg·L–1) + boric acid (100 mg·L–1) + sucrose (20 g·L–1) for 15 hours and maintained in glasshouses. Induction of roots was more effective with 125 mg·L–1 IBA supplemented with boric acid and sucrose. This treatment showed the highest frequency of rooting and the largest number of roots per cutting. The in vitro system of propagation was performed on the basal medium of Murashige and Skoog (MS), to which triadizuron (TDZ), benzyladeninepurine (BAP), and kinetin (Kin) were added in different combinations. TDZ was more effective than BAP or Kin in the promotion of shoot regeneration.