SSR assessment of Phytophthora infestans populations on tomato and potato in British gardens demonstrates high diversity but no evidence for host specialization

Phytophthora infestans populations can differ in composition as a result of host specialization on tomato and potato hosts. In Great Britain many amateur gardeners grow outdoor tomatoes but there is little or no commercial tomato production outdoors. This study analysed isolates of P. infestans from British gardens with 12 multiplexed simple sequence repeat markers that are used to monitor the disease on commercial potato crops. Samples of P. infestans from tomato hosts were collected in 3 years and from potato in 1 year from across Great Britain. Seven previously unreported clonal lineages were detected in garden populations and higher frequencies of unique clonal lineages (28–40%) were present compared with populations from British commercial potato crops reported elsewhere. Garden populations had a lower proportion (11–48% less) of the most common lineages (13_A2 and 6_A1) that together made up at least 86% of the commercial potato populations during the sampling period. Host species accounted for only 2·0% of molecular variance detected between garden potato‐ and tomato‐hosted samples. No significant difference in clonal lineage composition was found between host species in Great Britain and this could be due to the whole P. infestans population overwintering on potato. British garden populations on both hosts were much more diverse than those on commercial potato crops; this finding may be influenced by less frequent fungicide use by gardeners and a higher diversity of unsprayed susceptible potato cultivars, enabling metalaxyl‐sensitive and less aggressive genotypes to survive in gardens.     

New mutants of winter rapeseed (Brassica napus L.) with changed fatty acid composition

Seeds of the winter oilseed rape (Brassica napus L.) line PN 3756/93 were treated with ethyl methanesulphonate to induce mutations in the fatty acid biosynthetic pathway. The seed mutagenic treatment was repeated in the M₂ generation. After treatments, individual seed and plant selections were made for changes in fatty acid composition during several generations of inbreeding. Self‐pollinated plants with changed fatty acid compositions were inbred to obtain genetically homozygous and stable mutant lines. Two mutants, M‐10453 and M‐10464, with increased levels of oleic acid (approximately 76%) and reduced linoleic and linolenic acid contents (8.5% and 7.5%, respectively) were selected. Gene or genes controlling desaturation of oleic acid were probably mutated in these plants. The third mutant, M‐681 had a very low linolenic acid content (approximately 2.6%) and increased linoleic acid content (approximately 26%). This would suggest the occurrence of mutations in genes controlling linoleic acid desaturation. The results of selection work during several generations showed that the environment had substantial influence on the composition of seed oil. This made the search for mutants with modify fatty acid compositions difficult. The induced mutants are not directly usable as new varieties, but can be used as parents in crosses for the development of high quality rapeseed varieties.     

Linkage relationships among loci controlling morphological traits in cowpea (Vigna unguiculata (L.) Walp.)

Summary Linkage among loci controlling various morphological traits in cowpea were determined using F₂ progenies. Data were collected on individual plants of four crosses segregating for several loci. Recombination estimates between the following pairs of loci were as follows: Sw (swollen vs normal stem base)-Fbc (cream vs green flower buds) (41±4.8%), Pu^s(purple vs green stems)-Cbr (cocoa-brown vs straw-yellow dry pods) (31±5.7%), Pu^p(purple vs green immature pods)-Cbr (30±5.7%), Pu^s-Pu^p (4±1.5%), Ndt (non-determinate vs determinate)-Pd (peduncle colour) (26±2.8%), Ndt-Hg (semi-erect vs erect plant type) (26±2.8%), P^t(purple vs green pod tips)-Bk (greyish-black vs straw-yellow dry pods) (19±2.4%) and Hg-Bpd (normal vs branching peduncle (24±9.5%). Four linkage groups (LG) were identified in these studies. The proposed LG I contained loci Sw and Fbc; LG II loci Pu^s, Pu^p, and Cbr; LG III loci Pd, Ndt, Gh, and Bpd; and LG IV loci P^tand Bk.     

Cytoplasmic relatedness of apple landraces and cultivars: a molecular analysis

Summary Mitochondrial DNA (mtDNA) diversity has been determined in apple landraces and cultivars, based upon restriction fragment length polymorphisms (RFLPs) for several mitochondrial genes. Our analysis includes three cultivars, Golden Delicious, McIntosh and Delicious, which represent the various patterns of mtDNA polymorphisms previously described (Ishikawa et al., 1992). A total of five RFLPs were detected, allowing classification of the apple genotypes into four cytoplasmic groups: GroupI, Golden Delicious-type; GroupII, McIntosh-type; GroupIII, Delicious-type; and Group IV, Dolgo Crab-type. European landraces and cultivars were assigned to Groups I, II, and III, while chinese crab apples were placed in either Group III or IV.     

Effects of length of ensiling and maturity group on chemical composition and in vitro ruminal degradability of whole‐crop maize

Nine hybrids (three maturity groups, dry matter 343 ± 5.6 g/kg) of whole‐crop maize were ensiled in eight replicates in laboratory‐scale silos. Each hybrid was sampled at harvest and after 30, 60, 90 and 120 days (d) of ensiling. Samples were analysed for chemical composition (proximate constituents, fermentation products and pH), starch, non‐protein N (NPN) and NH₃‐N. Each sample and its neutral detergent fibre (NDF) fraction were incubated in the Hohenheim gas test system. In vitro gas production was measured after 0, 2, 4, 8, 12, 16, 24, 36, 48, 72 and 96 hr of incubation. Gas production of the neutral detergent soluble (NDS) fraction (mainly starch) was calculated using a curve subtraction method. Gas production dynamics over time were estimated using a nonlinear regression equation; afterwards, a two‐factorial analysis of variance (storage length, maturity group and their interaction) using the general linear models procedure was conducted. After 30 d, all silages were well fermented. Most fermentation products and proximate constituents only changed until 30 or maximum 60 d of ensiling. Only few changes in in vitro nutrient degradability were detected after the first 30 d or as influenced by maturity group. Ensiling per se increased the ruminal degradability of the NDS, but there was no further increase caused by a prolonged duration of storage. However, extensive changes in crude protein fractions occurred with a linear increase in NPN and NH₃‐N compounds from 0 to 120 d of storage, indicating continual protein and amino acid degradation.     

Random amplified polymorphic DNA analyses of cytoplasmic male sterile and male fertile Pigeonpea (Cajanus cajan (L.) Millsp.)

Randomly amplified polymorphic DNA (RAPD) markers were used for the identification of two pigeonpea cytoplasmic genic male sterile (CMS) lines derived from crosses between the wild (Cajanus scarabaeoides & C. sericeus) and the cultivated species of Cajanus cajan. The male sterile (A) line and its maintainer (B) line could be easily differentiated with certain random primers. The two male sterile (288 A and 67 A)systems are based on C. scarabaeoidesand the other is based on C. sericeus could also be differentiated. Amplification product of 600bp amplified by primer OPC-11 was observed in both the cytoplasmic male sterile lines (288 A and 67A), which was absent in the maintainer lines (288 B and 67 B) and the putative R-line (TRR 5 and TRR 6). CMS lines, putative R lines, other cultivars and wild species under the study could be easily distinguished with the help of different primers. Dendrogram constructed based on the similarity index showed that considerable genetic variation exist sbetween CMS lines, two putative R line and wild species studied. This revised version was published online in July 2006 with corrections to the Cover Date.     

The distribution and interrelationship of collapse,volumetric shrinkage,moisture content and density in trees of Eucalyptus regnans F. Muell.

Summary The relationships among collapse, volumetric shrinkage, moisture content and basic density and their distribution within the stem were examined for trees of E. regnans. It was found that collapse and volumetric shrinkage each were significantly related to moisture content (positively), basic density (negatively), and (positively) to the derived values P (per cent of theoretical saturation) and Q (per cent of cell cavity volume containing water). Notwithstanding the inverse association evident between moisture content and density in the living tree, moisture content was shown to be independently related to each of collapse and volumetric shrinkage.Within the stem, collapse and volumetric shrinkage were negatively correlated with height in the tree although the significance of this relationship was qualified by the adjustment for other variables. Samples containing sapwood displayed collapse values significantly lower than heartwood samples. This was reflected in the presence of a positive relationship between collapse and distance from the periphery when all material was considered, but a negative relationship when sapwood-containing samples were omitted. Basic density was positively correlated with height in the tree and negatively correlated with distance from the periphery. Moisture content, P and Q were negatively correlated with both height in the tree and distance from the periphery although the latter relationship for moisture content was dependent on adjustment for density.The highly significant relationship between volumetric shrinkage and collapse suggested that the former could confidently be used in assessing collapse severity. Moisture content was determined to be an independent indirect indicator of collapse whereas basic density, P, Q and green density could all be of indicatory value, especially the last in view of its ease of measurement.