Effect of phosphate and the arbuscular mycorrhizal fungus Glomus intraradices on disease severity of root rot of peas (Pisum sativum) caused by Aphanomyces euteiches

 The effects of inorganic phosphate levels and the presence of arbuscular mycorrhiza on disease severity of Aphanomyces euteiches in pea roots were studied. Disease severity on roots and epicotyl as well as the oospore number within infected root tissue were correlated with the phosphorus (P) level in the growth medium. The arbuscular mycorrhizal fungus Glomus intraradices increased P uptake and the P concentration in the plant but reduced disease development in peas. Polyacrylamide gel electrophoresis followed by densitometry of glucose-6-phosphate dehydrogenase specific to A.euteiches was used to measure the activity of the pathogen in roots. The enzyme activity increased with disease severity and disease incidence, except in plants supplemented with P at the highest level, where a peak in activity was seen 12 days after inoculation with the pathogen, followed by a decrease in activity. The epicotyl of mycorrhizal plants showed a reduction in disease severity although this part of the plants was not mycorrhizal. Thus, an induced systemic factor may be responsible for increased resistance in mycorrhizal plants. Accepted: 21 August 1998     

Application of Soil‐borne Actinomycetes for Biological Control against Fusarium Wilt of Chickpea (Cicer arietinum) caused by Fusarium solani fsp pisi

Black root rot, caused by Fusarium solani f.sp. pisi, is a devastating soil‐borne disease in chickpea in Iran with no effective control measures. With the aim of finding applicable biocontrol agents to alleviate the malady, isolates of Actinomycetes isolated from soil and their antagonistic effect against F. solani f.sp. pisi were evaluated both in vitro and in vivo. More than 100 Actinomycetes isolates were screened for their antifungal activities against the pathogen. The most active isolates were evaluated in greenhouse for their biocontrol performance. Based on the results of dual cultures in screening evaluations, the size of inhibition zone of fungal growth, and the most effective antagonist isolates (S3, S12 and S40) were selected for further studies. Identity of active isolates was determined, in this regard, 16S rDNA of isolates were amplified using universal bacterial primers FD1 and RP2. The PCR products were purified and sequenced. Sequence analysis of 16S rDNA was then performed using NCBI BLAST method. Comparison of the near full length 16S rRNA sequence of isolates to GenBank sequences demonstrated that isolates S3 and S12 were most similar to Streptomyces antibioticus, while isolate S40 was most similar to Streptomyces peruviensis. Biocontrol studies of these isolates in control of the disease in greenhouse significantly decreased the disease severity. Actinomycetes isolate S12 demonstrated the greatest effect in reducing disease than the other two. Results of this research are at preliminary stage for developing biocontrol agents. These data can be utilized as a platform for future studies with the aim of commercializing these biocontrol products and hoping to step towards sustainable agriculture.     

Identification of ‘Candidatus Phytoplasma asteris' (16SrI‐B) Causing Witches' Broom Disease of Mallotus japonicus in Korea

Mallotus japonicus with witches' broom disease were observed in Jeollabuk‐do, Korea. A phytoplasma from the infected leaves was identified, based on the 16S rDNA, 16S‐23S intergenic spacer region, and fragment of rp operon and tuf gene sequences. The 16S rDNA sequences exhibited maximum (99.7%) similarity with Iranian lettuce phytoplasma, the rp operon sequences exhibited 100% similarity with Goldenrain stunt phytoplasma, and the tuf gene sequences exhibited 99.8% similarity with Japanese spurge yellows phytoplasma. Results of the sequence analysis and phylogenetic studies confirmed that the phytoplasma associated with M. japonicus in Korea was an isolate of Aster Yellows group (subgroup16SrI‐B).     

The potential use of papyrus (Cyperus papyrus L.) wetlands as a source of biomass energy for sub‐Saharan Africa

Four of five people in sub‐Saharan Africa rely on the traditional use of solid biomass, mainly fuelwood, for cooking. In some areas, the current rate of fuelwood consumption will exhaust biomass reserves within the next decade or two. A largely unrecognized source of biomass are tropical wetland ecosystems which have been shown to be some of the most productive ecosystems globally, exhibiting rates of net primary productivity comparable with high‐input, intensively managed agricultural systems. Papyrus (Cyperus papyrus L.) is an emergent sedge with C₄ photosynthesis which is native to the wetlands, river valleys and lakes of central, eastern and southern Africa. The mean standing dry matter of culms and umbels measured at a number of locations throughout East Africa is 38.3 ± 21.6 tDM ha^?1, and the aerial net primary productivity ranges between 25.9 and 136.4 tDM ha^?1 yr^?1. Papyrus vegetation can be harvested by hand and stacked on the rhizome mat for partial air‐drying, and it has been demonstrated that an annual harvesting regime has no negative impacts on long‐term productivity. The use of papyrus as a biofuel for cooking and heating depends on converting it to a suitably combustible form, such as compressed or carbonized briquettes with a calorific value approximately one‐third less than wood charcoal. While papyrus has significant potential as a biofuel, we argue that an integrated management and decision‐making framework for the sustainable utilization of papyrus wetlands is required, in which all ecosystem services including the provision of biomass energy need to be assessed. Sustainability of papyrus wetlands requires management which combines the strength of traditional communal governance and modern legislation to promote its utilization. In this way, local communities can benefit from the inherent advantages of tropical wetlands as very productive ecosystems.     

Knockout of two BnaMAX1 homologs by CRISPR/Cas9‐targeted mutagenesis improves plant architecture and increases yield in rapeseed (Brassica napus L.)

Plant height and branch number are essential components of rapeseed plant architecture and are directly correlated with its yield. Presently, improvement of plant architecture is a major challenge in rapeseed breeding. In this study, we first verified that the two rapeseed BnaMAX1 genes had redundant functions resembling those of Arabidopsis MAX1, which regulates plant height and axillary bud outgrowth. Therefore, we designed two sgRNAs to edit these BnaMAX1 homologs using the CRISPR/Cas9 system. The T₀ plants were edited very efficiently (56.30%–67.38%) at the BnaMAX1 target sites resulting in homozygous, heterozygous, bi‐allelic and chimeric mutations. Transmission tests revealed that the mutations were passed on to the T₁ and T₂ progeny. We also obtained transgene‐free lines created by the CRISPR/Cas9 editing, and no mutations were detected in potential off‐target sites. Notably, simultaneous knockout of all four BnaMAX1 alleles resulted in semi‐dwarf and increased branching phenotypes with more siliques, contributing to increased yield per plant relative to wild type. Therefore, these semi‐dwarf and increased branching characteristics have the potential to help construct a rapeseed ideotype. Significantly, the editing resources obtained in our study provide desirable germplasm for further breeding of high yield in rapeseed.     

Limber pine (Pinus flexilis James) genetic map constructed by exome‐seq provides insight into the evolution of disease resistance and a genomic resource for genomics‐based breeding

Limber pine ( Pinus flexilis ) is a keystone species of high‐elevation forest ecosystems of western North America, but some parts of the geographic range have high infection and mortality from the non‐native white pine blister rust caused by Cronartium ribicola . Genetic maps can provide essential knowledge for understanding genetic disease resistance as well as local adaptation to changing climates. Exome‐seq was performed to construct high‐density genetic maps in two seed families. Composite maps positioned 9612 unigenes across 12 linkage groups ( LG s). Syntenic analysis of genome structure revealed that the majority of orthologs were positional orthologous genes ( POG s) with localization on homologous LG s among conifer species. Gene ontology ( GO) enrichment analysis showed relatively fewer constraints for POG s with putative roles in adaptation to environments and relatively more conservation for POG s with roles in basic cell function and maintenance. The mapped genes included 639 nucleotide‐binding site leucine‐rich repeat genes ( NBS ‐ LRR s) , 290 receptor‐like protein kinase genes ( RLK s), and 1014 genes with potential roles in the defense response and induced systemic resistance to attack by pathogens. Orthologous loci for resistance to rust pathogens were identified and were co‐positioned with multiple members of the R gene family, revealing the evolutionary pressure acting upon them. This high‐density genetic map provides a genomic resource and practical tool for breeding and genetic conservation programs, with applications in genome‐wide association studies ( GWASs ), the characterization of functional genes underlying complex traits, and the sequencing and assembly of the full‐length genomes of limber pine and related Pinus species.     

Assessment of microbial diversity in the rhizosphere of Pinus roxburghii (Sarg.) and bio‐inoculant potential of selected pine bacterial isolates for wheat varieties based on cultureindependent and culture‐dependent techniques

• Evidence is lacking regarding compatibility of pine bacteria as bio‐inoculants for crops. The diversity and abundance of rhizosphere bacteria of Pinus roxburghii has never been investigated with simultaneous application of culture‐dependent and culture‐independent techniques. The present study was aimed to isolate, characterise, check the bio‐inoculant potential of pine bacteria and assess rhizosphere bacterial diversity using culture‐independent advanced approaches.
• Forty bacteria isolated from the rhizoplane of P. roxburghii growing in a cold climate at high altitude in Murree, were morphologically characterised; nine were identified by 16S rRNA sequence analyses and used in experiments. Diversity and abundance of the 16S rRNA gene and nif H gene in the rhizosphere was assessed by cloning, RFLP analysis, 454‐amplicon pyrosequencing and qPCR.
• The bacterial isolates significantly improved dry weight of shoot, root, root area, IAA and GA₃ content, number of grains plant^?1, weight of grains plant^?1 in wheat varieties Chakwal‐50 and Fareed‐06 under axenic and field conditions. The number of 16S rRNA sequences (2979) identified by pyrosequencing shared similarity with 13 phyla of bacteria and archaea.
• The results confirm the existence of diverse bacteria of agricultural and industrial importance in the rhizosphere and compatibility of rhizoplane bacteria as bio‐inoculants for wheat varieties.