Phenotypic examination of variation occurring both among families and among genotypes within a T. repens x (T. ambiguum x T. occidentale) BC₁F₂ hybrid population : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Plant Breeding at Massey University, Palmerston North, New Zealand

Development of white clover cultivars with increased vegetative persistence, particularly in dryland farming systems has been a major goal within breeding programmes, however little useful genetic variation for survival and growth in these environments has been found. Consequently, it has become necessary to look towards white clovers wild relatives as sources of genetic variation. T. repens x (T. ambiguum x T. occidentale) tri-species hybrids have been developed, however, their morphologies have not been evaluated, and little is known about optimal breeding strategies in these populations. An experiment was designed to characterise the magnitude of phenotypic variation for a range of root, shoot, and floral traits, and to ascertain optimal breeding strategies within a T. repens x (T. ambiguum x T. occidentale) BC1F2 hybrid plant population. The experiment was designed such that it could be analysed in two ways; a) Investigated levels of phenotypic variation occurring among hybrid families, compared to representatives of their F1 parents b) Investigated levels of phenotypic variation among individual hybrid genotypes, again compared to representatives of their F1 parents. Analysis (a) found a relative lack of among hybrid family variation. With significant (P<0.05) family variance components for 11 of the 18 traits measured, and generally only occurring between the upper and lower extremes. Repeatability estimates on a family mean basis were low (less than 0.51 for all traits). Analysis (b) found significant (P<0.05) genotypic variance components for all of the traits measured. Repeatability estimates ranged from 0.47-0.88, indicating a relatively high level of genetic determination for the majority of traits. Pattern analysis allowed the identification of hybrid genotypes showing the combined expression of key shoot, and root traits. These genotypes may provide a route to hybrid clover cultivars showing increased vegetative persistence via increased nodal and tap-root size, combined with good dry matter production

Comparative growth and management of white and red clovers

peer-reviewedThe aim of this paper is to provide the underpinning scientific basis for the optimum management of white and red clovers. Critical morphological and canopy characteristics which influence the yield and persistence of white and red clover in swards, and how management factors (choice of cultivar, defoliation and nitrogen (N) fertilizer) modify these are considered. Canopy development is vitally important as it determines the extent to which a) light is intercepted for photosynthesis needed for growth and b) the base of the sward is deprived of the red component in daylight, inhibiting branching of stolons and crowns in white and red clover, respectively. The role of cultivar, defoliation and N fertilizer in determining yield and persistence of the two legumes, mainly in mixtures with grass, are discussed principally in terms of morphological development and exploitation of light. It is concluded that optimum management for grass/white clover places emphasis on building up stolons and maximising contribution of clover leaf area to the upper layers of the mixed canopy and, while red clover is more competitive to grass than white clover, that benefit is lost when a grass/red clover sward is grazed

The Impact of the Long-Distance Transport of a BEL1-Like Messenger RNA on Development

BEL1- and KNOTTED1-type proteins are transcription factors from the three-amino-loop-extension superclass that interact in a tandem complex to regulate the expression of target genes. In potato (Solanum tuberosum), StBEL5 and its Knox protein partner regulate tuberization by targeting genes that control growth. RNA movement assays demonstrated that StBEL5 transcripts move through the phloem to stolon tips, the site of tuber induction. StBEL5 messenger RNA originates in the leaf, and its movement to stolons is induced by a short-day photoperiod. Here, we report the movement of StBEL5 RNA to roots correlated with increased growth, changes in morphology, and accumulation of GA2-oxidase1, YUCCA1a, and ISOPENTENYL TRANSFERASE transcripts. Transcription of StBEL5 in leaves is induced by light but insensitive to photoperiod, whereas in stolon tips growing in the dark, promoter activity is enhanced by short days. The heterodimer of StBEL5 and POTH1, a KNOTTED1-type transcription factor, binds to a tandem TTGAC-TTGAC motif that is essential for regulating transcription. The discovery of an inverted tandem motif in the StBEL5 promoter with TTGAC motifs on opposite strands may explain the induction of StBEL5 promoter activity in stolon tips under short days. Using transgenic potato lines, deletion of one of the TTGAC motifs from the StBEL5 promoter results in the reduction of GUS activity in new tubers and roots. Gel-shift assays demonstrate BEL5/POTH1 binding specificity to the motifs present in the StBEL5 promoter and a double tandem motif present in the StGA2-oxidase1 promoter. These results suggest that, in addition to tuberization, the movement of StBEL5 messenger RNA regulates other aspects of vegetative development.Fil: Lin, Tian. University of Iowa; Estados UnidosFil: Sharma, Pooja. University of Iowa; Estados UnidosFil: Gonzalez, Daniel Hector. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Agrobiotecnología del Litoral. Universidad Nacional del Litoral. Instituto de Agrobiotecnología del Litoral; ArgentinaFil: Viola, Ivana Lorena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Agrobiotecnología del Litoral. Universidad Nacional del Litoral. Instituto de Agrobiotecnología del Litoral; ArgentinaFil: Hannapel, David J.. University of Iowa; Estados Unido

Do forage legumes have a role in modern dairy farming systems?

peer-reviewedIntensification in New Zealand dairy farming systems has placed greater pressure on clover performance and fitness and has highlighted the need to develop clover cultivars that are better adapted to intensive grazing systems. Increased stocking rates and increased use of nitrogen fertiliser have put enormous pressure on the contribution of clover to modern dairy systems. Future innovations such as semi-hybrid cultivars offer the potential to improve the competitiveness of legumes with nitrogen-fertilised forage grasses. Similarly, advances in condensed tannin research suggest that significant animal performance gains can be achieved in conjunction with reduced environmental impact. In order to capture these benefits, dairy farmers will need to reassess their grazing management to ensure that legumes can be maintained at economically useful levels. Novel grazing management systems that optimise the benefits provided by the grass and legume components need to be used in future dairy farming systems. Forage legumes, and especially white clover, have an important role to play in modern dairy systems

Comparison of production systems for potato (Solanum tuberosum L.) minituber production with different cultivars : a thesis submitted in partial fulfilment of the requirements for the degree of Master of Applied Science in Nursery Production

The purpose of these studies is to determine the effect of different production systems (Aeroponic (AP), Deep flow (DF), Nutrition film technique (NFT) and Bark) on production of first generation (prebasic) potato (Solanum tuberosum L.) minitubers with different cultivars (Russet Burbank, Rua, Kenebec, Atlantic and Diésrée). Prebasic tubers usually multiplied in a greenhouse in a bark medium. Replacing the bark based system by a highly intensive aeroponic system is viable. The aeroponic system significantly produced higher tuber numbers per plant and produced a higher percentage (82%) of 1 -2g size tuber than other systems evaluated. In aeroponic and deep flow systems, the time to tuberization is higher. When tuberization is delayed, stolons grow continuously in the deep flow and aeroponic systems. In hydroponic systems a developing stolons did not encounter sufficient mechanical resistance to limit growth, they grew extremely vigorously and very wide of diameter (1.92- 2.42 mm). When roots and stolons filled the aeroponic and deep flow containers some root rustication occurred then tubers were initiated. Acid treatment efficiently synchronised tuberization in the aeroponic systems, tubers were visible four days after acid treatment. Optimum acid treatment depends on the specific cultivar or stage of stolon development. Rua produced the highest yield per plant and highest tuber number per plant. The pH and treatment time significantly affected the tuber number per plant. Acid treatment at pH 3.5 produced the highest tuber number (19.8) per plant. Minitubers show a dormant period immediately after they are harvested. Application of GA is a useful method to break minituber dormancy. Fifty percentage of the GA treated tubers sprouted within 20 days after treatment, while untreated control took 37 days. Overall, sprouting was highest for 100 ppm treatment, but was not significantly different from 30 ppm. The highest and lowest sprouting cultivars were Russet Burbank and Atlantic respectively. Potato cuttings can be propagated in an aeroponic system. Application of IBA treatment at 0.1 to 0.3% significantly induced root formation and root growth. About 80% of the IBA treated cuttings rooted and produced longer roots than untreated cuttings. From these studies we found the aeroponic system to be suitable for minituber production as well as the propagation of potato cuttings. Production of high tuber number per plant in aeroponic systems will reduced the production cost and reduce the number of field multiplications required before final cropping

Vegetative Spread of Dioecious Hydrilla Colonies in Experimental Ponds

Stolon formation and fragmentation are two vegetative mechanisms by which hydrilla colonies expand. These two mechanisms of spread were studied in ponds located in Lewisville, TX over a two-year period. Stolons were determined to be the predominant mechanism for localized expansion in undisturbed areas. While some fragments were produced, they accounted for only 0.1% of the establishment of rooted plants in new quadrats. Peak production of fragments occurred in October and November, with fragment densities of 0.15 N m-2 d-1. Expansion by stolons occurred between June and November of each year, with higher rates of spread (up to 4.0 cm d-1 radial growth) observed in the second season

Aspects of management options for pasture-based dairy production stocked at two cows per hectare

End of project reportWhite clover in association with Rhizobium bacteria have the capacity to fix or convent atmospheric N into plant available N. This can make a considerable contribution to sward productivity. One of the objectives of this experiment was to determine the upper carrying capacity of grass-white clover swards receiving 90 kg fertilizer N/ha. A second objective was to examine the impact of grass-clover swards on mineral-N in the soil and losses of nitrate-N from soil to drainage water during the winter. This experiment was conducted at Solohead Research Farm. There were three treatments: (i) A grass-only treatment (FN) stocked at 2.0 cows per ha in 2003 and 2.2 cows per ha during 2004, 2005 and 2006. This treatment received an average of 226 kg per ha of fertilizer N per year during these years. (ii) A grass-clover treatment (WC) stocked at the same rates as FN and received an average of 90 kg per ha of fertilizer N per year during the experiment. (iii) A grass-only treatment (CC) that was gradually converted over to grass-clover during the experiment and stocked at 2.0 cows per ha throughout the experiment. Fertilizer N input was gradually lowered from 150 kg per ha in 2003 to a target of 90 kg per ha in 2005 and 2006

How Planting Density Affects Number and Yield of Potato Minitubers in a Commercial Glasshouse Production System

Commercial potato minituber production systems aim at high tuber numbers per plant. This study investigated by which mechanisms planting density (25.0, 62.5 and 145.8 plants/m2) of in vitro derived plantlets affected minituber yield and minituber number per plantlet. Lowering planting density resulted in a slower increase in soil cover by the leaves and reduced the accumulated intercepted radiation (AIR). It initially also reduced light use efficiency (LUE) and harvest index, and thus tuber weights per m2. At the commercial harvest 10 weeks after planting (WAP), LUE tended to be higher at lower densities. This compensated for the lower AIR and led to only slightly lower tuber yields. Lowering planting density increased tuber numbers per (planted) plantlet in all grades. It improved plantlet survival and increased stem numbers per plant. However, fewer stolons were produced per stem, whereas stolon numbers per plant were not affected. At lower densities, more tubers were initiated per stolon and the balance between initiation and later resorption of tubers was more favourable. Early interplant competition was thought to reduce the number of tubers initiated at higher densities, whereas later-occurring interplant competition resulted in a large fraction of the initiated tubers being resorbed at intermediate planting densities. At low planting densities, the high number of tubers initiated was also retained. Shortening of the production period could be considered at higher planting densities, because tuber number in the commercial grade > 9 mm did not increase any more after 6 WA

Phenotypic evaluation of Trifolium repens x Trifolium uniflorum F₁ interspecific hybrids as predictors of BC₁ hybrid progeny : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Plant Breeding at Massey University, Palmerston North, New Zealand

Interspecific hybrids between white clover (Trifolium repens) and its close relatives are being created to address the lack of variation within white clover for traits relating to persistence and drought tolerance. This study addresses two concepts related to developing hybrid breeding strategies using Trifolium repens x Trifolium uniflorum hybrids. A first sandframe experiment investigated whether some of the first generation hybrid plants (F1) with common parents were better than others as future parents. A second experiment assessed whether the performance of the first back cross (BC1) progenies could be predicted from the parental F1 phenotypes. The foliage, fertility, roots and dry weight production of four families of F1 hybrids were evaluated following a period of growth in sand. From each family, the F1 hybrids with the highest and lowest dry weight production were selected and back crossed to two contrasting white clover cultivars. The resulting BC1 hybrid phenotypes were evaluated to ascertain whether any F1 hybrids were markedly better as future parents in hybrid breeding programmes, and whether the F1 phenotype could be used to predict that of the BC1 progeny. Differences in expression of more than half of the traits evaluated were found both between F1 families, and among genotypes within F1 families. Evaluation of the subsequent BC1 generation identified large amounts of variation in expression of most traits both within and among hybrid families. However correlations between trait expression of the F1 parent and the corresponding BC1 progeny were weak to non-existent for most traits evaluated. The absence of correlations indicated that the performance of an F1 hybrid genotype is not able to be used as a predictor of the BC1 progeny phenotypes, and that selection out of the F1 generation is futile in the formation of interspecific hybrid breeding populations