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The hrp/wts gene cluster of Pantoea stewartii subsp. stewartii is required for pathogenicity on sweet corn and the ability to elicit a hypersensitive response (HR) in tobacco. Site-directed transposon mutagenesis and nucleotide sequencing were used to identify hrp/wts genes within the left 20 kb of this cluster. Seventeen open reading frames (ORFs) comprise seven genetic complementation groups. These ORFs share homology with hrp and dsp genes from Erwinia amylovora, Erwinia chrysanthemi, and Pseudomonas syringae pathovars and have been designated, in map order, wtsF, wtsE, hrpN, hrpV, hrpT, hrcC, hrpG, hrpF, hrpE, hrpD, hrcJ, hrpB, hrpA, hrpS, hrpY, hrpX, and hrpL. Putative hrp consensus promoter sequences were identified upstream of hrpA, hrpF, hrpN, and wtsE. Expression of the hrpA, hrpC, and wtsE operons was regulated by HrpS. Transposon mutations in all of the hrp operons abolished pathogenicity and HR elicitation, except for the hrpN and hrpV mutants, which were still pathogenic. hrpS, hrpXY, and hrpL regulatory mutations abolished HrpN synthesis, whereas secretory mutations in the hrpC, hrpA, and hrpJ operons permitted intracellular HrpN synthesis. wtsEF mutants were not pathogenic but still produced HrpN and elicited the HR. wtsE encodes a 201-kDa protein that is similar to DspE in E. amylovora and AvrE in P. syringae pv. tomato, suggesting that this protein is a major virulence factor involved in the elicitation of water-soaked lesions.

Wild relatives are a potential source of genetic diversity to lentil {Lens culinaris Medik). The objective of this research was to obtain viable interspecific hybrids between the domesticated lentil and its wild relatives.The paper details the results of a number of interspecific crosses among L. culinaris, L. orientalis, L. odemensis, L. ervoides and L. nigricans. Viable hybrids were produced between L. culinaris x L. orientalis, L. culinaris x L. nigricans, L. culinaris x L. ervoides and between L. culinaris x L. odemensis. Further viable hybrids were obtained between L. culinaris and L. ervoides, which have the potential to be a 'bridge' in hybridization to L. culinaris for specific L. nicrigans lines which proved recalcitrant in L. culinaris x L. nigricans crosses. This is the first time that four wild species of lentils have been used successfully in hybridization with cultivated lentils, and viable hybrids produced. This paper also suggests that the artificial supplement of GA, hormone is needed after fertilization for the normal growth ofthe hybrid embryo, possibly as the natural GA, production is restricted with alien pollinations in cultivated lentils in both F, and backcross hybrids.

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Stripe rust of wheat caused by Puccinia striiformis West. f. sp. tritici presents a serious problem for wheat production worldwide, and identification and deployment of resistance sources to it are key objectives for many wheat breeders. Here we report the detection of simple sequence repeat (SSR) markers linked to the durable adult plant resistance of cv. ÔOtaneÕ, which has conferred this resistance since its release in New Zealand in 1984. A double haploid population from a cross between ÔOtaneÕ and the susceptible cv. ÔTiriteaÕ was visually assessed for adult plant infection types (IT) in the glasshouse and field, and for final disease severity in the field against stripe rust pathotype 106E139A + . At least three resistance loci controlled adult plant resistance to stripe rust in this population. Quantitative trait loci (QTL) mapping results revealed that two of these, one on chromosome 7DS corresponds to the durable adult plant resistance gene Yr18 and other on chromosome 5DL were contributed from ÔOtaneÕ; while the remaining one on chromosome 7BL, was contributed from the susceptible ÔTiriteaÕ. Interval mapping placed the ÔOtaneÕ-resistant segment near the centromere of chromosome 7DS at a distance of 7 cM from the SSR marker gwm44. The stability of QTL in the two environments is discussed. SSR gwm44 is potentially a candidate marker for identifying the durable resistance gene Yr18 in breeding programmes.

Pantoea stewartii subsp. stewartii causes Stewart's wilt of sweet corn. A hypersensitive response and pathogenicity (Hrp) secretion system is needed to produce water-soaking and wilting symptoms in corn and to cause a hypersensitive response (HR) in tobacco. Sequencing of the hrp cluster revealed a putative harpin gene, hrpN. The product of this gene was overexpressed in Escherichia coli and shown to elicit the HR in tobacco and systemic resistance in radishes. The protein was designated HrpN(Pnss). Like other harpins, it was heat stable and protease sensitive, although it was three- to fourfold less active biologically than Erwinia amylovora harpin. We used antibodies to purified HrpN(Pnss) to verify that hrpN mutants could not produce harpin. This protein was secreted into the culture supernatant and was produced by strains of P. stewartii subsp. indologenes. In order to determine the importance of HrpN(Pnss) in pathogenesis on sweet corn, three hrpN::Tn5 mutants were compared with the wild-type strain with 50% effective dose, disease severity, response time, and growth rate in planta as parameters. In all tests, HrpN(Pnss) was not required for infection, growth, or virulence in corn or endophytic growth in related grasses.

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