No abstract

An indirect phenotyping method was developed in order to estimate the susceptibility of rubber tree clonal varieties to Corynespora Leaf Fall (CLF) disease caused by the ascomycete Corynespora cassiicola. This method consists in quantifying the impact of fungal exudates on detached leaves by measuring the induced electrolyte leakage (EL%). The tested exudates were either crude culture filtrates from diverse C. cassiicola isolates or the purified cassiicolin (Cas1), a small secreted effector protein produced by the aggressive isolate CCP. The test was found to be quantitative, with the EL% response proportional to toxin concentration. For eight clones tested with two aggressive isolates, the EL% response to the filtrates positively correlated to the response induced by conidial inoculation. The toxicity test applied to 18 clones using 13 toxinic treatments evidenced an important variability among clones and treatments, with a significant additional clone x treatment interaction effect. A genetic linkage map was built using 306 microsatellite markers, from the F1 population of the PB260 x RRIM600 family. Phenotyping of the population for sensitivity to the purified Cas1 effector and to culture filtrates from seven C. cassiicola isolates revealed a polygenic determinism, with six QTL detected on five chromosomes and percentages of explained phenotypic variance varying from 11 to 17%. Two common QTL were identified for the CCP filtrate and the purified cassiicolin, suggesting that Cas1 may be the main effector of CCP filtrate toxicity. The CCP filtrate clearly contrasted with all other filtrates. The toxicity test based on Electrolyte Leakage Measurement offers the opportunity to assess the sensitivity of rubber genotypes to C. cassiicola exudates or purified effectors for genetic investigations and early selection, without risk of spreading the fungus in plantations. However, the power of this test for predicting field susceptibility of rubber clones to CLF will have to be further investigated.

Corynespora cassiicola is an ascomycete fungus causing important damages in a wide range of plant hosts, including rubber tree. The small secreted protein cassiicolin is suspected to play a role in the onset of the disease in rubber tree, based on toxicity and gene expression profiles. However, its exact contribution to virulence, compared to other putative effectors, remains unclear.We created a deletion mutant targeting the cassiicolin gene Cas1 from the highly aggressive isolate CCP. Wild-type CCP and mutant ccpΔcas1 did not differ in terms of mycelium growth, sporulation, and germination rate in vitro. Cas1 gene deletion induced a complete loss Version postprint

Among 14 strains of yellow-pigmented acid- and alcohol-fast rods isolated from human pathological materials, 10 strains from tuberculoid lesions of cervical or facial lymphadenitis in children merit particular interest. They were compared with some of the mycobacteria, including Mycobacterium tuberculosis, and with Nocardia. On the basis of morphology, staining properties, cultural characteristics, pathogenicity, and allergic reactions in laboratory animals, they have been placed in the genus Mycobacterium. However, the degree and quality of their differences from other named species of the genus as observed under the present experimental conditions, and the fact of their isolation in pure culture from closed lesions, has led to the proposal that they be given the name Mycobacterium scrofulaceum n. sp.

Rubber trees are the main source of natural rubber (NR). The area occupied by rubber plantations rose from 3.9 million ha in 1961 to 12.5 million ha in 2018. Both the expansion of rubber plantations in marginal zones (prone to biotic and abiotic stress), and long-term rubber tree cultivation in traditional areas, raise questions about the sustainability of NR production in a context of climate change. Our study set out to gain insights into the biogeochemical cycles in rubber plantations, for a better matching of fertilizer inputs to the dynamics of nutrient demand throughout rubber tree growth. Nutrient accumulation in tree biomass is a major component of the biological cycle in tree plantations. We studied the dynamics of biomass and nutrient accumulation in two chronosequences covering the whole lifespan of a plantation in Ivory Coast managed on a sandy soil at the SAPH site, and one on a clayey soil at the SOGB site. In total, 56 trees were destructively sampled in 2-, 5-, 20-and roughly 40-year-old stands. While the use of allometric relationships is common for estimating nutrient stocks in planted forests, this study was the first to provide allometric equations predicting nutrient stocks in rubber tree components. Allometric models were applied to the inventory of 4 commercial stands, for each age at each site, to estimate stand biomass and nutrient stocks. The current annual increments of nutrient stocks in tree biomass peaked between 2 and 5 years after planting. They reached 80 kg ha-1 yr-1 for N, 14 kg ha-1 yr-1 for P and 34 kg ha-1 yr-1 for K at SAPH (53, 7, and 39 kg ha-1 yr-1 respectively at SOGB), which highlighted the importance of an appropriate fertilization schedule for young rubber trees. At the clear-cut age (38-40 years), the amounts of nutrients accumulated in tree biomass were 970 kg N ha-1 , 188 kg P ha-1 , 366 kg K ha-1 , 941 kg Ca ha-1 and 255 kg Mg ha-1 on the sandy soil at SAPH (907,118, 629 1499, and 375 kg ha-1 respectively on the clayey soil at SOGB). Contrasting soil properties and management practices at the two sites had a much greater effect on the amounts of P, K, Ca and Mg accumulated in the trees than on N accumulation. Logging practices in rubber plantations can lead to considerable nutrient exports on poor tropical soils. Harvest residues should be distributed uniformly in the plots so that the roots of young trees can quickly gain access to the nutrients released during decomposition.