Search

Phytopathogenic bacteria inject effector proteins into plant host cells to promote disease. Plant resistance (R) genes encoding nucleotide-binding leucine-rich repeat (NLR) proteins mediate the recognition of functionally and structurally diverse microbial effectors, including transcription-activator like effectors (TALEs) from the bacterial genus Xanthomonas. TALEs bind to plant promoters and transcriptionally activate either disease-promoting host susceptibility (S) genes or cell death-inducing executor-type R genes. It is perplexing that plants contain TALE-perceiving executor-type R genes in addition to NLRs that also mediate the recognition of TALE-containing xanthomonads. We present recent findings on the evolvability of TALEs, which suggest that the native function of executors is not in plant immunity, but possibly in the regulation of developmentally controlled programmed cell death (PCD) processes.

Xanthomonas arboricola is an important bacterial species, the pathovars of which are responsible for bacterial blight diseases on stone fruit, hazelnut, Persian walnut, poplar, strawberry, poinsettia and banana. In this study, we evaluated variable number tandem repeats (VNTR) as a molecular typing tool for assessing the genetic diversity within pathovars of X. arboricola. Screening of the X. arboricola pv. pruni genome sequence (CFBP5530 strain) predicted 51 candidate VNTR loci. Primer pairs for polymerase chain reaction (PCR) amplification of all 51 loci were designed, and their discriminatory power was initially evaluated with a core collection of 8 X. arboricola strains representative of the different pathovars. Next, the 26 polymorphic VNTR loci present in all strains were used for genotyping a collection of 61 strains. MLVA is a typing method that clearly differentiates X. arboricola strains. The MLVA scheme described in this study is a rapid and reliable molecular typing tool that can be used for further epidemiological studies of bacterial diseases caused by X. arboricola pathovars. (C) 2014 Elsevier B.V. All rights reserved.

Despite efforts to control late blight in potatoes by introducing R pi -genes from wild species into cultivated potato, there are still concerns regarding the durability and level of resistance. Pyramiding R pi -genes can be a solution to increase both durability and level of resistance. In this study, two resistance genes, R Pi-mcd1 and R Pi-ber, introgressed from the wild tuber-bearing potato species Solanum microdontum and S. berthaultii were combined in a diploid S. tuberosum population. Individual genotypes from this population were classified after four groups, carrying no R pi -gene, with only R Pi-mcd1, with only R Pi-ber, and a group with the pyramided R Pi-mcd1 and R Pi-ber by means of tightly linked molecular markers. The levels of resistance between the groups were compared in a field experiment in 2007. The group with R Pi-mcd1 showed a significant delay to reach 50% infection of the leaf area of 3 days. The group with R Pi-ber showed a delay of 3 weeks. The resistance level in the pyramid group suggested an additive effect of R Pi-mcd1 with R Pi-ber. This suggests that potato breeding can benefit from combining individual R pi -genes, irrespective of the weak effect of R Pi-mcd1 or the strong effect of R Pi-ber.

Information on fertilizer response in cassava in Africa is scarce. We conducted a series of on-farm and on-station trials in two consecutive years to quantify yield responses of cassava to mineral fertilizer in Kenya and Uganda and to evaluate factors governing the responses. Average unfertilized yields ranged from 4.2 to 25.7 t ha-1 between sites and years. Mineral fertilizer use increased yields significantly, but response to fertilizer was highly variable (- 0.2 to 15.3 t ha-1). Average yield response per kg applied nutrient was 37, 168 and 45 and 106, 482 and 128 kg fresh yield per kg of applied N, P and K, respectively in 2004 and 2005. Fertilizer response was governed by soil fertility, rainfall and weed management, but was not influenced by variety, pest and disease pressure and harvest age. Relative N and K yields were positively correlated to SOC and exchangeable K, while response to fertilizer decreased on more fertile soils. Still, fertilizer response varied widely on low fertility soils (e.g. on soils with