BackgroundMost agronomic plant traits result from complex molecular networks involving multiple genes and from environmental factors. One such trait is the enzymatic discoloration of fruit and tuber tissues initiated by mechanical impact (bruising). Tuber susceptibility to bruising is a complex trait of the cultivated potato (Solanum tuberosum) that is crucial for crop quality. As phenotypic evaluation of bruising is cumbersome, the application of diagnostic molecular markers would empower the selection of low bruising potato varieties. The genetic factors and molecular networks underlying enzymatic tissue discoloration are sparsely known. Hitherto there is no association study dealing with tuber bruising and diagnostic markers for enzymatic discoloration are rare.ResultsThe natural genetic diversity for bruising susceptibility was evaluated in elite middle European potato germplasm in order to elucidate its molecular basis. Association genetics using a candidate gene approach identified allelic variants in genes that function in tuber bruising and enzymatic browning. Two hundred and five tetraploid potato varieties and breeding clones related by descent were evaluated for two years in six environments for tuber bruising susceptibility, specific gravity, yield, shape and plant maturity. Correlations were found between different traits. In total 362 polymorphic DNA fragments, derived from 33 candidate genes and 29 SSR loci, were scored in the population and tested for association with the traits using a mixed model approach, which takes into account population structure and kinship. Twenty one highly significant (p < 0.001) and robust marker-trait associations were identified.ConclusionsThe observed trait correlations and associated marker fragments provide new insight in the molecular basis of bruising susceptibility and its natural variation. The markers diagnostic for increased or decreased bruising susceptibility will facilitate the combination of superior alleles in breeding programs. In addition, this study presents novel candidates that might control enzymatic tissue discoloration and tuber bruising. Their validation and characterization will increase the knowledge about the underlying biological processes.

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The metabolism of the plant protectant Nemacur (1; common name fenamiphos) was investigated in 16 soils from 11 countries with different climates. The metabolism study was conducted under aerobic conditions at two different temperatures. The active ingredient used was phenyl ring-l-14C-labeled. In all soils the degradation products fenamiphos sulfoxide (21, fenamiphos sulfone (31, 3-methyl-4-(methylsulfiny1)phenol (51, 3-methyl-4-(methylsulfonyl)phenol (61, and 3-methyl-4-(methylsulfonyl)-anisole (7) as well as 14C02 could be detected in various amounts. Although the soils had been selected for their diverse heterogeneity, the degradation pathway was the same in all soils. After incubation for 90 days a t a temperature of 22 "C, between 2.3% and 66.8% of the total toxic residues (TTR; 1 + 2 + 3) were still detectable in the soil. During this period, 1.1-39.0s of the applied radioactivity was mineralized and between 18.5% and 61.8% bound to the soils. After application and incubation of 1%-labeled metabolites 3-methyl-4-(methylsulfinyl)phenol(5), 3-methyl-4-(methylsulfonyl)phenol(6), and 3-methyl-4-(methylthio)phenol (4), in a Parabraunerde from Germany, a large proportion of the radioactivity was no longer extractable.