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A spontaneous mutant, Abs, that does not abscise any organs despite an apparently normal pattern of growth and senescence was isolated from among plants of Lupinus angustifolius cv. 'Danja'. Abs was found to be a recessive single gene mutation, and it was proposed that the gene for the original mutant phenotype, referred to as Abs, be designated abs1. An artificially induced mutant allelic to abs1 was also obtained and a non-allelic mutant phenotype, Delabs (delayed abscission), which was designated abs2. Morphological and cytological features of the abscission process under conditions of natural and ethylene-induced senescence were compared in the wild-type parent and Abs mutant. In the parent genotype abscission under natural conditions is similar to many other species, consisting of a stage of cell division forming an abscission zone, activation of the cytoplasm of zone cells, dissolution of the middle lamella, disorganization of fibrillar wall structure, and cell separation. A slightly different pattern of abscission zone development was observed for ethylene-treated explants of the parent, mainly with respect to features of cell division and cell enlargement. In Abs no abscission occurred for any abscission sites under conditions of natural senescence or with ethylene treatment of small shoot explants. However, relatively normal abscission zones were differentiated at all sites in the mutant except that extensive cell wall disorganization did not occur. Ethylene production by leaves or other organs of the mutant was no different from that of Danja. Application of copper salts or hydrogen peroxide, droughting, waterlogging, or application of abscisic acid (ABA) increased ethylene production equally in both genotypes but did not result in abscission in the mutant. Release of root cap border cells, the only other cell separation process examined, was similar in each genotype. The study concludes that the mutation is quite specific to the abscission process and may be due to a lack of or delay in the expression of hydrolytic enzyme(s) associated specifically with abscission zone differentiation and separation.

Erwinia amylovora causes fire blight, a disease responsible for enormous economic losses in the pome fruit-producing areas where it is present. Despite the abundant research on fire blight, information about E. amylovora population dynamics and survival in fire blight cankers and the plant defense responses to this pathogen in the infected bark are limited. In our study, we obtained fire blight cankers in apple, pear, and Asian pear cultivars showing differing resistance to the disease by shoot inoculation with E. amylovora. We collected cankers from irrigated and non-irrigated trees every 3 months in two independent field experiments and analyzed samples by viability digital PCR. We also assessed the expression of pathogenicity-related (PR) genes in the bark of selected apple and Asian pear cultivars. A logistic regression analysis revealed the impact of environmental and host factors on E. amylovora detection rates in cankers. The chances of detecting live E. amylovora cells in cankers increased significantly in those collected from irrigated trees, in July, and/or during an experiment performed in a year with an expected average rainfall when compared to samples from non-irrigated trees, collected in January, and/or during an experiment performed under environmental conditions dominated by drought. We found a positive correlation between the pathogen detection rates in cankers and the host resistance to fire blight that might be explained by lower E. amylovora survival rates in more damaged tissues of susceptible hosts. The genes PR-1, PR-2, PR-5, and PR-8 were induced in the bark surrounding apple and Asian pear fire blight cankers. Our study, involving the analysis of more than 800 canker samples, provides new knowledge about the fire blight disease cycle and lays the foundation for improved fire blight management and eradication strategies in pome fruit orchards.

Background Narrow-leafed lupin is an emerging crop of significance in agriculture, livestock feed and human health food. However, its susceptibility to various diseases is a major obstacle towards increased adoption. Sclerotinia sclerotiorum and Botrytis cinerea – both necrotrophs with broad host-ranges - are reported among the top 10 lupin pathogens. Whole-genome sequencing and comparative genomics are useful tools to discover genes responsible for interactions between pathogens and their hosts. Results Genomes were assembled for one isolate of B. cinerea and two isolates of S. sclerotiorum , which were isolated from either narrow-leafed or pearl lupin species. Comparative genomics analysis between lupin-derived isolates and others isolated from alternate hosts was used to predict between 94 to 98 effector gene candidates from among their respective non-conserved gene contents. Conclusions Detection of minor differences between relatively recently-diverged isolates, originating from distinct regions and with hosts, may highlight novel or recent gene mutations and losses resulting from host adaptation in broad host-range fungal pathogens. Electronic supplementary material The online version of this article (10.1186/s12864-019-5774-2) contains supplementary material, which is available to authorized users.