Chapters authored
Advances in Plant Tolerance to Biotic Stresses
Plants being sessile in nature encounter numerous biotic agents, including bacteria, fungi, viruses, insects, nematodes and protists. A great number of publications indicate that biotic agents significantly reduce crop productivity, although there are some biotic agents that symbiotically or synergistically co-exist with plants. Nonetheless, scientists have made significant advances in understanding the plant defence mechanisms expressed against biotic stresses. These mechanisms range from anatomy, physiology, biochemistry, genetics, development and evolution to their associated molecular dynamics. Using model plants, e.g., Arabidopsis and rice, efforts to understand these mechanisms have led to the identification of representative candidate genes, quantitative trait loci (QTLs), proteins and metabolites associated with plant defences against biotic stresses. However, there are drawbacks and insufficiencies in precisely deciphering and deploying these mechanisms, including only modest adaptability of some identified genes or QTLs to changing stress factors. Thus, more systematic efforts are needed to explore and expand the development of biotic stress resistant germplasm. In this chapter, we provided a comprehensive overview and discussed plant defence mechanisms involving molecular and cellular adaptation to biotic stresses. The latest achievements and perspective on plant molecular responses to biotic stresses, including gene expression, and targeted functional analyses of the genes expressed against biotic stresses have been presented and discussed.
Part of the book: Plant Genomics
Advances in Plant Tolerance to Abiotic Stresses
During the last 50 years, it has been shown that abiotic stresses influence plant growth and crop production greatly, and crop yields have evidently stagnated or decreased in economically important crops, where only high inputs assure high yields. The recent manifesting effects of climate change are considered to have aggravated the negative effects of abiotic stresses on plant productivity. On the other hand, the complexity of plant mechanisms controlling important traits and the limited availability of germplasm for tolerance to certain stresses have restricted genetic advances in major crops for increased yields or for improved other traits. However, some level of success has been achieved in understanding crop tolerance to abiotic stresses; for instance, identification of abscisic acid (ABA) receptors (e.g., ABA-responsive element (ABRE) binding protein/ABRE binding factor (AREB/ABF) transcription factors), and other regulons (e.g., WRKYs, MYB/MYCs, NACs, HSFs, bZIPs and nuclear factor-Y (NF-Y)), has shown potential promise to improve plant tolerance to abiotic stresses. Apart from these major regulons, studies on the post-transcriptional regulation of stress-responsive genes have provided additional opportunities for addressing the molecular basis of cellular stress responses in plants. This chapter focuses on the progress in the study of plant tolerance to abiotic stresses, and describes the major tolerance pathways and implicated signaling factors that have been identified, so far. To link basic and applied research, genes and proteins that play functional roles in mitigating abiotic stress damage are summarized and discussed.
Part of the book: Plant Genomics
Cassava Bacterial Blight: A Devastating Disease of Cassava
Cassava (Manihot esculenta Crantz) with its long life cycle is affected by several diseases of which cassava bacterial blight (CBB) is the major bacterial disease in the cassava belt worldwide. The epidemiological and ecological investigations undertaken on the disease showed that the causal agent, the bacterium Xanthomonas axonopodis pv. manihotis (Xam), possesses several means for survival and dissemination that may play an important role as inoculum sources for the infection when favorable conditions occur, and the subsequent damage of the plant causing severe yield losses. In fact, Xam survives epiphytically on some weeds occurring in and around cassava fields without developing blight symptoms. Investigating the survival period over the seasons, a longer survival exceeding 5 months has been observed in non-decayed cassava debris. Also, some insects in cassava field like the variegated grasshopper (Zonocerus variegatus) vehicles the pathogen for some time. Over seasons Xam also survives often latently, in cassava stems which are then used for establishing new plantations. In regional disease surveys across ecozones in West Africa, no zone of preference has been found. Though, comparing the development of the disease and the damages caused in yield loss trials in two agro-eco-zones over 2 years, CBB was more pronounced and caused higher yield and biomass losses in the forest savannah transition zone than in the dry savannah where symptom development was positively correlated with the rainfall patterns. The detailed knowledge of the epidemiology, disease development, survival and dissemination, of the reaction of cassava varieties towards CBB such as physiological resistance mechanisms, identification of genetic resistance (QTL) and the background of observed field resistance as well as of the influence of planting time and cropping pattern allows to recommend integrated management measures such as sanitation, intercropping, removal of diseased leaves, management of planting dates according to ecozone, soil amendments, use of resistant genotypes.
Part of the book: Cassava