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    A comparative analysis of agronomic water-use efficiency and its proxy measures as derived from key morpho-physiological and supportive quantitative genetics attributes of perennial ryegrass under imposed drought
    (John Wiley and Sons Ltd and New Phytologist Foundation, 2023-10-10) Weerarathne LVY; Jahufer Z; Schäufele R; Lopez I; Matthew C
    Water-use efficiency (WUE) is an under-researched but very important drought tolerance trait in forage breeding. This research estimated quantitative genetic parameters of morpho-physiological traits linked to agronomic water-use efficiency (WUEA) and its proxy measures based on δ13C (WUEi) or gas exchange (evapotranspiration, WUEAET, or stomatal conductance WUEASC) of genotypes from half-sib families of Lolium perenne L. (PRG) in a simulated summer drought cycle. Principal component analysis (PCA) of trait data distinguished a group of PRG genotypes where high WUEA and dry matter yield was associated with deep rooting, leaf hydration at more negative leaf osmotic and water potential, and reduced soil moisture depletion. Plants with this trait association sustained net assimilation and postdefoliation regrowth in drought. However, WUEi, WUEASC, and WUEAET were poorly correlated with most traits of interest at p < .05. Another PCA revealed a weak association between WUEA and its proxy measures under conditions tested. Quantitative genetic parameters including high estimates of narrow-sense heritability (hn2>0.7;p<.05) of WUEA and related traits emphasized the genetic potential of the key trait combination for selecting PRG for improved drought tolerance. Research findings highlight the relative importance of WUEA and its proxy measures in the broad definition of PRG drought tolerance for breeding purposes
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    Comparative response of tall fescue (Lolium arundinacea Schreb.) and perennial ryegrass (Lolium perenne L.) swards to variation in defoliation interval and height : a thesis presented in partial fulfilment of the requirements for the degree of Master of AgriScience at Massey University
    (Massey University, 2015) Kaufononga, Salesi
    This thesis studies aspects of the epidemiology of Nematodirus spathiger and Nematodirus filicollis, both are common and potentially pathogenic parasites of lambs in New Zealand. Three studies were undertaken; the first a presence/absence survey to determine the distribution of the two species on farms, the second examined the prevalence of benzimidazole (BZ) resistance in the two species and the third experiment investigated the requirements for chilling for N. filicollis eggs to hatch. The first two studies utilised faecal samples from routine faecal egg counts and/or routine faecal egg count reduction testing on farms. To identify the Nematodirus species involved, eggs from these samples were chilled and then incubated to facilitate hatching of N. filicollis, before larvae were recovered. The identity of the larvae was determined using PCR of the ITS-2 region of rDNA. The third experiment used a bulk collection of N. filicollis from naturally infected lambs. Extracted eggs were incubated at temperatures between 2.7°C - 9.9°C, for up to 224 days. The proportion of eggs hatching was assessed against chill units. Chill units (degree-day) were calculated by subtracting the culture temperature from a constant threshold of 11°C and multiplying by the number of days for which the sample was cultured. In Study 1, N. spathiger was present on all farms tested, while N. filicollis was found on 76% of farms. Both species were distributed throughout New Zealand, with no regional differences. In Study 2, the BZ-resistance study, efficacies below 95% were recorded for N. spathiger and N. filicollis on 95% (20/21) and 40% (4/10) respectively of farms tested. In Study 3, the chilling experiment, the overall hatching of N. filicollis eggs was low, but increased with chill accumulation to plateau at about 11%, with 800-1000 chill units required for maximum hatching. In conclusion the two species of Nematodirus were commonly found on most New Zealand farms. The prevalence of BZ-resistance in N. filicollis was lower than that in N. spathiger. N. filicollis required a considerable period of chilling to enable hatching to occur and this will influence their epidemiology.