Abstract:
Drought stress severely impacts plant production worldwide, and is predicted to increasingly affect crop production due to climate change. One of the main strategies to cope with the changing environment is the development of new cultivars with an improved tolerance to drought stress. A study was initiated to compare mitotically induced tetraploid roses with their diploid counterparts for their drought stress tolerance. The first step in this research is the development of a screening method to evaluate segregation for drought tolerance in a diploid rose population. Therefore, drought tolerance was screened in 69 genotypes selected from the F1 population resulting from a R. ‘Yesterday’ × R. wichurana hybridisation. The plants were subjected to two different irrigation regimes, reducing the amount of water received by the drought stress group to less than 10% of an optimal amount given in the control group. Relative water content (RWC), leaf water potential (Ψ) and effective photochemical quantum yield of photosystem II (Y(II)) were measured, next to stomatal size and density, and leaf morphological characteristics. RWC and Ψ were good indicators for screening drought sensitivity of the genotypes. However, Y(II) did not prove to be a reliable screening method in this study. This approach allowed the selection of interesting rose genotypes for further characterisation and tetraploidisation, potentially forming the basis of future drought tolerant rose cultivars.|
Physiological and pollen-based screening of shrub roses for hot and drought environments
Raju Bheemanahalli, Bandara Gajanayake, Suresh Lokhande, Kulvir Singh, Ramdeo Seepaul, Pam Collins, K. Raja Reddy Abstract
Rose plants growing under natural conditions are exposed to unfavorable environmental conditions such as high temperature and drought, particularly around the blooming stage. This can reduce the reproductive potential and aesthetic value of commercial rose cultivars, which are often more sensitive to harsh conditions. Plants adjust to adverse environments by regulating several morpho-physiological and biochemical processes, which are the key to tolerance mechanisms. Thus, to examine genetic potential of 22 roses, we characterized 18 traits: gas exchange, leaf biophysical, pigments, and pollen germination characteristics using field-grown roses at the blooming stage. A broad genetic variability (P < 0.001) in all measured traits suggests that roses comprise heat- and drought-adaptive traits. A weak correlation between the pollen viability or germination and the pollen tube length at 38 °C signifying the complexity of reproductive processes. However, three rose cultivars, Moje Hammarberg, Carefree Spirit, and Lavender Meidiland had better pollen germination-related traits (25 %) along with high photosynthetic capacity (24 %) and pigment traits (22 %) compared with sensitive cultivars. The generated phenotypic data, along with reliable phenotyping methods and identified candidate cultivars, would help develop roses with enhanced resilience to stress for dry and hotter climates. http://bulbnrose.x10.mx/Roses/breeding/BheemRosePollen2021.html
Host Manipulation of Parasites: Within-Plant Variation as a Defense against Rapidly Evolving Pests
Thomas G. Whitham
“In comparison with the trypanosome, in which variability is highly adaptive and clonally derived from a single organism, similar variability has been demonstrated with clonal populations of potatoes (Shepard et al., 1980). Clonal populations regenerated from a single leaf-cell protoplasts of the potato cultivar Russet Burbank exhibited high variation in disease resistance characters, tuber shape, yield, maturity date, photoperiod requirements for flowering, and plant morphology. Although the genetic mechanisms have yet to be determined, it would appear that substantial genetic variation exists within individual plants (at least in expression). It also appears that the observed variation is stable, and the enhanced resistance to early blight and late blight suggests that the cloning techniques may be important to varietal improvement. Contrary to traditional logic, the cloning techniques with potatoes seem to produce more useful variability than has resulted from the past 50 yr of conventional breeding programs.”
