| Summary: | Early leaf spot (ELS) caused by Cercospora arachidicola, late leaf spot (LLS) caused by
Cercosporidium personatum, web blotch (WB) caused by Phoma arachidicola and rust
caused by Puccinia arachidis, are serious diseases of groundnut in South Africa. The
aims of this study were to evaluate ARC-GCI germplasm for resistance to the important
foliar diseases such as ELS, LLS, WB, and rust and to ascertain if cytoplasmic factors
influence the pattern of inheritance of resistance to ELS, LLS, and WB, testa colour and
mutations such as the one responsible for cupleaf phenotypes.
Twenty-one reciprocal crosses were made to study the cytoplasmic factors but the F1
progenies gave no evidence of cytoplasmic factors directly responsible for any of the
above-mentioned traits.
During 2003/04, 138 ARC-GCI germplasm entries were evaluated for resistance to ELS,
LLS, WB and rust at Potchefstroom (North West Province; Highveld), Burgershall
(Mpumalanga Province), Brits (North West Province), Vaalharts (Northern Cape
Province) and Cedara (Kwazulu Natal Province). No fungicides were used to control the
foliar diseases. In trials at Vaalharts, Cedara, and Burgershall entries 1, 10-13, 18-21, 23,
30, 52 and 56-58 were resistant to two of the three (LLS, WB, and rust) foliar diseases
and entries 18, 19 and 20 (best) to LLS, WB and rust. At Brits, Elite (E) and ICRISAT (I)
short/medium growth entries 8I and 7E, were resistant to LLS and WB and the long
growth entries 1E and 3E were resistant to WB, LLS and rust. In micro-plots at
Potchefstroom entries 6, 9, 10 and 13-15 were resistant to LLS and WB and in the brick
plots 1-3, 6 and 7 to ELS and LLS.
Entries with resistance to ELS, LLS, WB, and rust as well as other favourable traits, such
as a high yield and oleic acid percentage, from the 2003/04 trials were included in the
2004/05 trials for further assessment. All the entries were evaluated for resistance to ELS,
LLS, WB and rust, were graded and grouped by using the Canonical Variate Analysis
(CVA). From the results on the five locality trials (2004/05) medium growth entries 1, 3, 7, 10, 14, 15, 20-22, 26, 27, 30, 32 and 33 were resistant to three or four of the foliar
diseases, gave good yields and choice grade kernels. The CVA identified separate groups,
containing entries 3, 20, 21 and 32, with resistance to two or more foliar diseases and
with high yield. No choice grade entries were reported for unsound blemished and soiled
(UBS) kernels with an UBS>13%.
In the Elite short/medium trials at Brits (2004/05) entries 3 and 8 were resistant to rust, 1,
2, 4, 7, 11-13, 15, 17, 19-22, 24 and 25 gave choice grade kernels, and 10, 13 and 12 the
highest yield. Entries 1-6, and 8-15 (Elite long) were resistant to LLS, 1-15 to WB, and 1,
4 and 15 to rust, 4, 10 and 12 gave choice grade kernels and 4, 1 and 10 the highest
yields. ICRISAT (long) entries 5 and 7 gave choice grade kernels, and 1, 6 and 3 the
highest yields. The CVA identified the groups containing medium growth entries 10, 12,
13, 22 and 23, Elite long 1, 4, 10 and 15 and ICRISAT long 5, 8 and 9 as groups with
resistance to two or more foliar diseases (ELS, LLS, WB, and rust) and good yield.
Twenty-three medium and 11 long growth entries in the Elite trials at Vaalharts (an extra
trial planted where fungicides were used to control foliar diseases) gave choice grade
kernels and good yields.
In this study, some ARC-GCI germplasm entries were resistant to ELS, LLS, WB, and
rust, but climatic factors influenced the severity of infection. Foliar diseases lowered the
quality and grade of the kernels and resulted in lower yields. CVA simplifies the
evaluation and grouping of new germplasm entries and will save valuable research
resources.
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