Info

Mean ± S.E.

780 ± 290

180 ± 71

440±130

95 ± 43

tions. The second component axis (PC2) explained 21% of the total variation in agronomic traits recorded in this trial and its large scores were associated with taller plants, high ear placement and poor ear aspect scores. The third component axis (PC3) accounted for 14% of the total variation in agronomic traits recorded in this trial and its large scores were associated with a delay in silking, good husk cover and plant aspect scores but with poor ear aspect score. Grain yield of the inbred lines was negatively correlated with PC1 (r = -0.73, p < 0.0001) scores but not with PC2 (r = -0.24, p = 0.08) and PC3 (r = -0.12, p = 0.40) scores of the inbred lines. We found some inbred lines with high grain yields and negative PC1 scores, indicating that some of them accumulated less aflatoxin but also had good husk cover, plant aspect and ear aspect scores as well as lower levels of ear rot, leaf blight and leaf rust infections.

Screening elite germplasm for resistance to specific fungi Evaluating resistant lines under artificial field infection

Field tests of inbred lines identified in the kernel screening assay are critical for identifying the best lines with consistently low levels of aflatoxin accumulation. The ultimate phase in the identification of lines that consistently accumulate less aflatoxins is the exposure of such lines to many populations of A. flavus under as wide a range of environmental conditions as possible. Nine inbred lines selected for low levels of aflatoxin production based on the kernel-screening assay were evaluated with artificial inoculation in the field in Nigeria in 2003. Among these lines, 1823, TZMI104 and TZMI502 had low levels of aflatoxin contamination under field conditions (Table 5). These three lines along with 1368 and TZMI102 also were evaluated in 2004. Two of the three inbred lines (1823 and TZMI502) that had low aflatoxin levels in 2003 also had low levels of aflatoxin in 2004, indicating that the laboratory-based kernel screening assay can be used to reliably screen breeding material prior to testing under field conditions (Brown et al., 1999).

Screening elite germplasm for reduced fumonisin production

Mixed infections with A. flavus and F. verticillioides occur in maize under field conditions. Thus, any strategy to reduce mycotoxin accumulation also should identify sources of resistance to fumonisin accumulation and incorporate them into adapted germplasm. IITA is screening elite maize germplasm for reduced fumonisin accumulation. A replicated field trial of 58 elite inbred lines was conducted at Ibadan, Nigeria in 2003 and 2004, in which emerging silks were artificially inoculated with a spore suspension of an isolate of F. verti-cillioides. At Ikenne in 2003 the response to natural infection was evaluated. The inbred lines differed markedly in fumonisin accumulation at both locations and in both seasons. At Ibadan, mean fumonisin concentration in the grain ranged from 1.1 to 130 ^g/g in 2003 and from 0.2 to 99 ^g/g in 2004. At Ikenne, mean fumonisin concentration in the grain ranged from 0 to 120 ^g/g in 2003. The number of lines at Ibadan with < 5.0 ^g/g fumonisin was nine in 2003 and 21 in 2004. Thirty-five inbred lines had < 5 ^g/g fumonisin in the grain at Ikenne in 2003. Three inbred lines [(1368/S.A. Pub Lines36/1368)-2-2-2-B, KU1414xICAL 36-1xKU1414-6-1-B and (CIM 116 x TZMi 302 x CIM 116)-2-2-B] and a commercial hybrid (Oba Super I) had < 5 ^g/g fumonisin in the grain in both seasons at Ibadan and in the one season at Ikenne. These results re-emphasize the need to conduct multi-location and multi-season evaluations of genetic materials to identify sources of resistance with consistently low levels of fumonisin accumulation.

Conclusions

Maize inbred lines with consistently low aflatoxin levels after repeated evaluation in the laboratory and in the field could be used in the development of hybrids and synthetic varieties that can be deployed in farmers' fields to help reduce mycotoxin contamination. The new inbred lines also could be used to broaden and to diversify the genetic base of resistant germplasm in maize breeding programs. The advances made in identifying genetically similar lines with contrasting aflatoxin levels may enable the characterization of mechanisms responsible for lower levels of aflatoxin accumulation and the identification of candidate genes that underlie resistance to A. flavus infection and/or aflatoxin accumulation, access to novel variants, and the development of markers for rapid screening of breeding materials. Promising lines with low fumonisin accumulation also could be used in crosses with inbred lines that accumulate lower levels of aflatoxin to develop new lines with combined resistance to both fungal species and to lower the contamination levels of both of these very important mycotoxins.

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