Abstract
Early and late leaf spot are two devastating diseases of peanut (Arachis hypogaea L.) worldwide. The development of a fertile, cross-compatible synthetic amphidiploid, TxAG-6 ([A. batizocoi × (A. cardenasii × A. diogoi)]4x), opened novel opportunities for the introgression of wild alleles for disease and pest resistance into commercial cultivars. Twenty-seven interspecific lines selected from prior evaluation of an advanced backcross population were evaluated for resistance to early and late leaf spot, and for yield in two locations in Ghana in 2006 and 2007. Several interspecific lines had early leaf spot scores significantly lower than the susceptible parent, indicating that resistance to leaf spot had been successfully introgressed and retained after three cycles of backcrossing. Time to appearance of early leaf spot symptoms was less in the introgression lines than in susceptible check cultivars, but the opposite was true for late leaf spot. Selected lines from families 43-08, 43-09, 50-04, and 60-02 had significantly reduced leaf spot scores, while lines from families 43-09, 44-10, and 63-06 had high pod yields. One line combined both resistance to leaf spot and high pod yield, and several other useful lines were also identified. Results suggest that it is possible to break linkage drag for low yield that accompanies resistance. However, results also suggest that resistance was diluted in many of the breeding lines, likely a result of the multigenic nature of resistance. Future QTL analysis may be useful to identify alleles for resistance and allow recombination and pyramiding of resistance alleles while reducing linkage drag.
Highlights
Leaf spot (ELS) (caused by Passalora arachidicola (Hori) U Braun [Cercospora arachidicola S
The combined analyses of early leaf spot scores of the 27 interspecific lines, three susceptible check varieties, and recurrent parent Florunner (Table 1) over environments in Ghana indicated that 20 entries had lower area under disease progress curves (AUDPC)
AUDPCELS, AUDPC for early leaf spot; AUDPCLLS, AUDPC for late leaf spot; T50ELS, days to early leaf spot lesions on 50% of plants; T50LLS, days to appearance of late leaf spot; PODYIELD, pod yield per plot in kg ha−1. 2 *, significant at the p = 0.05 level of probability; **, significant at p = 0.01; *** significant at p = 0.001. 3 n.d., no data
Summary
Leaf spot (ELS) (caused by Passalora arachidicola (Hori) U Braun [Cercospora arachidicola S. Curtis] Deighton]) diseases are two of the most yield-limiting biotic stresses in peanut (Arachis hypogaea L.) production worldwide [1], causing yield losses of up to 50% [2,3] or even 70% in West Africa [4,5]. In the United States these diseases are controlled by fungicides, but application increases production costs by about 10% [7]. Effective control of these diseases for these farmers includes the use of host plant resistance
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