During laboratory and field experiments on Nacella concinna on the west coast of Admiralty Bay, King George Island (Antarctica) clear morphological and behavioural differences between two limpet forms (N. concinna polaris and N. concinna concinna) were found. They suggested presence of genetic divergence. AFLP (amplified fragment length polymorphism) profiling of N. concinna individuals representing the two forms revealed nearly 32% of polymorphic bands; only 2% of them differed between the forms. Our results suggest that the observed phenotypic variation seems to be a result of adaptation to environ− mental conditions and not of any genetic divergence.
Early blight disease caused by Alternaria sp. is one of the most devastating diseases of
Solanaceous crops widely distributed in Sudan. The aim of this study was to determine the
genetic variation among different Alternaria isolates recovered from different Solanaceae
crops showing typical symptoms of early blight disease. Infected leaves of tomato, potato,
eggplant and pepper were collected from different geographical zones in Sudan. The recovered
fungal isolates were identified to the genus level based on cultural and morphological
characteristics. Five representative isolates were sent to the CABI Bioscience, U.K. for confirmation.
The genetic relationship among the isolates was determined using the amplified
fragments length polymorphism (AFLP) technique and the generated data were used to
create similarity matrices using the PAST 3.01 software package. Dendrograms were constructed
based on Jaccard’s similarity coefficients. A total of 70 fungal isolates was recovered
from the tested plants and all of them showed morphological characteristics typical
of Alternaria spp. The conidia appeared in multiple-branched chains with spore sizes in
the range of 2.38−13.09 μm × 12.30−43.63 μm. Therefore, the isolates were identified as
Alternaria alternata (Fr.) Keissl. The identification was then confirmed by CABI.AFLPbased
dendrogram which revealed five clusters with a significant cophenetic correlation
coefficient (r = 0.834) between the dendrogram and the original similarity matrix irrespective
of their geographical origins. Eighteen (75%) of the Alternaria isolated from tomato
leaves were clustered together in cluster I and five isolates formed two separate clusters,
viz. cluster IV (T-Kh5 and T-H1) and cluster V (T-H4 and T-Med2). The remaining isolate,
T-Am5, grouped with one of the potato isolates in cluster III. The other isolates which were
recovered from potato, pepper and eggplants were all separated from the tomato isolates
in the largest cluster.