03532nam a2200229 a 450000100080000000500110000800800410001910000190006024501210007926000400020030000090024050000180024952029180026765000190318565000170320465000150322165000170323665000090325365300130326265300150327565300120329014443112010-09-02       1978    bl uuuu  m   00u1 u    #d1 aDALL'AGNOL, A.  aSelecting soybean (Glycine max (L.) Merrill genotypes for resistance to the root-knot nematode Meloidogyne javanica.  a[S.l.]: University of Floridac1978  a33p.  aM.Sc. Thesis.  aPlant parasitic nematodes are major pests of soybeans (Glycine max L. Merr.) throughout the world. The root-knot species Meloidogyne javanica is a major pest in part of Southeastern USA and in many tropical areas. The most practical method for nematode control is resistant cultivars. Developing resistant cultivars is expensive. Improved techniques are needed to more precisely determine the reaction of soybean genotypes to specific nematodes. The purpose of this study was: a) to evaluate the feasibility of using frequently occurring checks to reduce the number of replications required, b) to determine how previous nematode selection pressures influenced resistance to M. javanica, and c) to estimate the amount resistance was increased by one generation of selection. Associations between gall scores and seed mottling and plant vigor scores were also determined.  We used 145, 384, and 1455 soybean genotypes all derived from Forrest c (Cobb x D68-216) in Experiments i, II, and III, respectively. Genotypes were evaluated in 1976 and 1977 at Live Oak, Florida, on Kendrich fine sand soil infested with M. javanica. Plot size was one hill planted with 7 to 10 seeds. Hills were 45 cm apart in rows 90 cm apart with 60 hills per row. Gall ratings were made in mid-September (growth stage R4 to R5). In Experiment I, adjusted scores gave more precision, but not enough more to justify the use of frequently occurring checks because nearly all field variation was blocked into replication effects. When variation within replication was increased by reassigning plots to two new replications, adjusted scores nearly the precision of raw scores. Thus, adjusted scores serve best in experiments where within replication differences are large. In Experiment II previous selection for resistance to M. incognita and Heterodera glycine did not improve average resistance to M. javanica. Howerver, plants selected in 1975 for resistance to M. javanica were significantly more resistant than unselected genotypes. The 1975 selection was from bulk populations. Plants were chosen for good seed production and little or no evidence of galling on roots of mature plants. Data from Experiment III showed that a second cycle of selection further increased resistance. Only 37% of the 1455 progenies, selected from bulk populations in 1975 received average scores of 1 or 2 in 1976. However, among 227 progenies selected for the best combination of gall scores (1, 2 or 3) and agronomic qualities, 66% received average scores pf 1 or 2 in 1977. A highly significant negative correlation between gall scores and mottling scores of planting seed indicated that plants produced from mottled seed tend to produce fewer and smaller galls. The highly significant correlation between plant vigor scores and gall scores suggests that many highly susceptible genotypes can be eliminated on the basis of plant vigor characteristics.  aplant breeding  aMelhoramento  aNematóide  aResistência  aSoja  aNematode  aResistance  aSoybean