Which way forward in the quest for drought tolerance in perennial ryegrass?

Pasture moisture stress for “summer” (November to March) was calculated for five main pastoral regions of New Zealand, and 9 or 10 years’ weather data were modelled in each case. Amelioration of water deficit with deeper rooting, stronger plant tissue osmotic potential for greater water extraction, or increased photosynthetic water use efficiency (WUE) was also modelled. Regional mean summer moisture deficits ranged from 34 mm in Taranaki to 447 mm in Canterbury. For a 10-cm increase in rooting depth, the model predicted an additional 16 mm water extraction. Increased plant osmotic potential was predicted to only slightly increase water extraction and paradoxically reduce yield. The assumed increase in photosynthetic WUE improved production by 240 kg DM ha-1 for the same water use. Drought tolerance traits exhibited by a range of ryegrass cultivars were measured in a series of glasshouse experiments and the potential to improve New Zealand ryegrass drought tolerance by introgression with germplasm originating from North Africa was assessed. North African germplasm possesses a trait of deep rootedness but has low summer productivity as a soil moisture conservation strategy and a high percentage of tillers flowering, so initial evaluations of this material for suitability for use in New Zealand are not promising. Ryegrass cultivars incorporating germplasm of Spanish origin appear to maintain summer production with enhanced WUE. Keywords: drought tolerance, root depth, Lolium perenne, perennial ryegrass, water defici

Which way forward in the quest for drought tolerance in perennial ryegrass?

Pasture moisture stress for “summer” (November to March) was calculated for five main pastoral regions of New Zealand, and 9 or 10 years’ weather data were modelled in each case. Amelioration of water deficit with deeper rooting, stronger plant tissue osmotic potential for greater water extraction, or increased photosynthetic water use efficiency (WUE) was also modelled. Regional mean summer moisture deficits ranged from 34 mm in Taranaki to 447 mm in Canterbury. For a 10-cm increase in rooting depth, the model predicted an additional 16 mm water extraction. Increased plant osmotic potential was predicted to only slightly increase water extraction and paradoxically reduce yield. The assumed increase in photosynthetic WUE improved production by 240 kg DM ha-1 for the same water use. Drought tolerance traits exhibited by a range of ryegrass cultivars were measured in a series of glasshouse experiments and the potential to improve New Zealand ryegrass drought tolerance by introgression with germplasm originating from North Africa was assessed. North African germplasm possesses a trait of deep rootedness but has low summer productivity as a soil moisture conservation strategy and a high percentage of tillers flowering, so initial evaluations of this material for suitability for use in New Zealand are not promising. Ryegrass cultivars incorporating germplasm of Spanish origin appear to maintain summer production with enhanced WUE. Keywords: drought tolerance, root depth, Lolium perenne, perennial ryegrass, water defici

Necrotroph Attacks on Plants: Wanton Destruction or Covert Extortion?

Necrotrophic pathogens cause major pre- and post-harvest diseases in numerous agronomic and horticultural crops inflicting significant economic losses. In contrast to biotrophs, obligate plant parasites that infect and feed on living cells, necrotrophs promote the destruction of host cells to feed on their contents. This difference underpins the divergent pathogenesis strategies and plant immune responses to biotrophic and necrotrophic infections. This chapter focuses on Arabidopsis immunity to necrotrophic pathogens. The strategies of infection, virulence and suppression of host defenses recruited by necrotrophs and the variation in host resistance mechanisms are highlighted. The multiplicity of intraspecific virulence factors and species diversity in necrotrophic organisms corresponds to variations in host resistance strategies. Resistance to host-specific necrotophs is monogenic whereas defense against broad host necrotrophs is complex, requiring the involvement of many genes and pathways for full resistance. Mechanisms and components of immunity such as the role of plant hormones, secondary metabolites, and pathogenesis proteins are presented. We will discuss the current state of knowledge of Arabidopsis immune responses to necrotrophic pathogens, the interactions of these responses with other defense pathways, and contemplate on the directions of future research