CREEPING CLOVER (Trifolium repens L.): BIOLOGICAL FEATURES, ECONOMIC SIGNIFICANCE, VARIETIES AND METHODS OF SEED PRODUCTION WHEN GROWN IN GRASS MIXTURES WITH A CEREAL COMPONENT

Creeping clover (Trifolium repens L.) is one of the best crops for creating meadow and pasture agrophytocenoses of long-term use. The biological features of this crop, such as durability, good yield, resistance to grazing, high leafiness, along with good feed quality indicators, its high protein nutritional value, make it indispensable when creating pastures not only in Russia, but also abroad. Creeping clover is one of the main components of grass mixtures for improving pastures and developing fallow lands; it is also an excellent phyto-meliorative crop that restores soil fertility. The most important problem of creeping clover seed production is harvesting due to the short stature of pasture varieties. Therefore, it is recommended to grow creeping clover for seeds in a mixture of grass together with cereal components such as perennial ryegrass, reed fescue, meadow fescue, etc. Due to the use of biological nitrogen of the legume component, energy consumption for the production of 1 kg of cereal grass seeds is reduced by 20–30% in comparison with uncoverless single-species crops. In addition to clover seeds, growing in grass mixtures allows you to get high yields of grass seeds in the second year of use without the use of nitrogen fertilizers.

The phytosanitary risks posed by seeds for sowing trade networks

When successful, the operation of local and international networks of crop seed distribution or “seed systems” ensures farmer access to seed and impacts rural livelihoods and food security. Farmers are both consumers and producers in seed systems and benefit from access to global markets. However, phytosanitary measures and seed purity tests are also needed to maintain seed quality and prevent the spread of costly weeds, pests and diseases, in some countries regulatory controls have been in place since the 1800s. Nevertheless, seed contaminants are internationally implicated in between 7% and 37% of the invasive plant species and many of the agricultural pests and diseases. We assess biosecurity risk across international seed trade networks of forage crops using models of contaminant spread that integrate network connectivity and trade volume. To stochastically model hypothetical contaminants through global seed trade networks, realistic dispersal probabilities were estimated from quarantine weed seed detections and incursions from border security interception data in New Zealand. For our test case we use contaminants linked to the global trade of ryegrass and clover seed. Between 2014 and 2018 only four quarantine weed species (222 species and several genera are on the quarantine schedule) warranting risk mitigation were detected at the border. Quarantine weeds were rare considering that average import volumes were over 190 tonnes for ryegrass and clover, but 105 unregulated contaminant species were allowed in. Ryegrass and clover seed imports each led to one post-border weed incursion response over 20 years. Trade reports revealed complex global seed trade networks spanning >134 (ryegrass) and >110 (clover) countries. Simulations showed contaminants could disperse to as many as 50 (clover) or 80 (ryegrass) countries within 10 time-steps. Risk assessed via network models differed 18% (ryegrass) or 48% (clover) of the time compared to risk assessed on trade volumes. We conclude that biosecurity risk is driven by network position, the number of trading connections and trade volume. Risk mitigation measures could involve the use of more comprehensive lists of regulated species, comprehensive inspection protocols, or the addition of field surveillance at farms where seed is planted.

A chronology of subterranean clover burr detachment mechanics and implications for seed harvestability

Seed retention has not been evaluated for subterranean clover ( Trifolium subterraneum L.), because its geocarpic seed-bearing burrs are currently harvested by suction systems. Development of improved harvest methods requires knowledge of subterranean clover seed retention characteristics and their changes with plant development. This study evaluates burr attachment and peduncle tensile strength during burr maturity until plant senescence across the three subspecies: subterraneum (cv. Dalkeith), yanninicum (cv. Monti) and brachycalycinum (cv. Mawson). Peduncle tensile strength was greater than burr-to-peduncle attachment strength for each subspecies, with peak mean peduncle strength 30–130% greater than peak mean burr-to-peduncle attachment strength. Both strength measurements decreased significantly (greater than 50% for each subspecies) as the plant senesced, which was associated with reductions in burr moisture content, and burr and peduncle diameters. Microscopy indicated a ductile to brittle transition as peduncles senesced, reducing energy absorption and increasing the likelihood of failure at defects. These results are important for the commercial production of subterranean clover seed and suggest it may be possible to harvest seed before plant senescence with dig-invert machinery, similar to that used for peanut harvesting. However, this approach would require harvesting prior to maximum seed development and the implications for seed viability and yield need to be further evaluated.

Dispersal and spatiotemporal distribution of Protapion fulvipes in white clover fields: implications for pest management

Yield loss caused by insect pests remains a substantial problem in agriculture. Chemical control, with potential negative effects on non-target organisms, is still the main tool for pest management. For pest species with limited dispersal capacity, rotation of the crop in time and space has potential as an alternative management measure. This is particularly important in organic farming, where most agrochemicals are prohibited, but also relevant as a complementary pest management strategy in conventional agriculture. Clover is an important crop used for animal feed and as green manure; however, seed-eating weevils can severely limit the seed yield. We hypothesized that the previous year’s clover seed fields constitute the major sources of weevil pests. Consequently, a greater distance to, and a smaller pest load from, this source should reduce the number of weevils colonizing the new seed fields. To map population dynamics and dispersal range of Protapion fulvipes, an economically important seed weevil specialized on white clover, we conducted field studies over four years in 45 white clover seed fields. We found that P. fulvipes overwinters close to its source field and disperses to new fields in early spring the following year. Pest abundance increased with pest load in the previous year’s seed field, but decreased by 68% per km distance to the previous year’s field. Thus, separation of seed production fields between years by 2–3 km would create a spatiotemporal pest management tool to reduce the pest infestation below the estimated economic injury level.

The Effects of Red Clover Seed Treatment with Cold Plasma and Electromagnetic Field on Germination and Seedling Growth Are Dependent on Seed Color

This study aimed to estimate the effects of cold plasma (CP) and electromagnetic field (EMF) treatment of red clover (Trifolium pratense) seeds with different coat colors on germination kinetics, the content of seed phytohormones, and the growth of seedlings. Seeds of red clover cultivar ‘Arimaiciai’ were treated with radio-frequency EMF or capacitively coupled low-pressure CP for different durations. There were no differences in germination kinetics between yellow, brown, and dark purple seeds in control, but the germination rate of seeds treated with CP and EMF depended on seed color: The germination of yellow seeds was stimulated stronger compared to dark purple and brown seeds, and EMF did not stimulate germination in brown seeds. The content of phytohormones in control seeds and the shift in their amount induced by seed treatments were also strongly dependent on seed color. No relationship was found between the effect on germination kinetics and changes in phytohormone levels. In the control, seedlings growing from the yellow seeds were heavier, and the number of root nodules was 12.5 times larger compared to seedlings of dark purple seeds. Seed treatments with CP and EMF significantly increased the number of root nodules, and this effect was stronger in seedlings from dark purple seeds compared to those from yellow seeds.

Review of seed yield components and pollination conditions in red clover (Trifolium pratense L.) seed production

Red clover (Trifolium pratense L.) is an important forage legume grown in many of the temperate regions around the world. In order to evaluate possible causes for the low seed yield in particular in tetraploid red clover, we surveyed 71 studies of red clover seed production published from 1948 to 2019, reviewing seed yield components, pollination and reproductive traits. Seed yield components are recorded to contribute to and improve our understanding of the complex processes leading to the red clover seed yield. However, the measurement approaches varied largely among the studies, depending on whether the seed yield components are directly measured or calculated. Red clover seed production is dependent on insect pollen transfer. However, much uncertainty of pollination and reproductive success remains. Pollination conditions were often neglected: one third of the papers did not mention pollination conditions. The information that connects pollination and seed set are lacking, very few studies measured traits in floral morphology, ovule fertilisation and seed maturation. We suggest that consistent and comprehensive evaluation of pollination and reproductive success are required to improve our understanding of reasons for the low seed yield in red clover and hence the possibilities for future improvement.

Harvesting subterranean clover seed – current practices, technology and issues

Subterranean clover (Trifolium subterraneum L.) is Australia’s most widely sown annual pasture legume. Its widespread use as a pasture plant requires a well-functioning seed production industry, and Australia is the only significant producer of subterranean clover seed globally. However, the sustainability of this industry is under threat due to its reliance on ageing harvest equipment and the resultant environmental impacts. In order to evaluate seed harvesting practices, technology, and issues, we report on case studies, workshops, and a survey of seed producers across southern Australia. The Horwood Bagshaw Clover Harvester, designed in the 1950s, remains the most popular subterranean clover seed harvester. We discuss its use and modifications, and document several contemporary issues facing the seed production industry. Issues are primarily soil erosion and degradation; the expensive, slow and labour-intensive harvest process; and poor reliability and maintainability of harvesters that are now at least 30 years old. We conclude the root cause of these issues is the suction harvest technology utilised by the Horwood Bagshaw Clover Harvester. Analysis of the current harvest system is provided to support the development of new approaches to harvest subterranean clover seeds.

Phenotypic traits for wild red clover seed yield under drought conditions

Changes in the gene pool and homogeneity of red clover cultivars occur over time. Therefore, it is necessary to constantly renew the breeding material and foundation seed. Moreover, the market also prescribes a new demand. Based on the Natura 2000 habitats profile, we collected seeds from 39 locations across Lithuania in 2016. The phenotypic traits that affect the seed yield of red clover were analysed in 2018. The homogeneity of the populations with reference to the seed yield and 1 000 seed weight (TSW) were determined as well. Also, the possibility of obtaining two seed yields per season under drought conditions from wild genotypes of red clover was analysed. We found that the final seed yield mostly depends on the seed number per flower head (SN/FH), which strongly correlated with 1^st component of PCA during first (r = 0.91) and second (0.92) harvest. Meanwhile, the cluster analysis showed that the typical wild red clover has a lower seed weight than the cultivars and could be clustered on the basis of seed homogeneity. Finally, based on the seed phenotype and harvest components, there were five prospective accessions (2177, 2871, 2876, 2898 and 2899) for a new cultivar prototype.

RESEARCH OF DESIGN AND TECHNOLOGICAL PARAMETERS OF CLEANING CLOVER SEEDS BY COLOR SORTING

The article presents the results of study to establish the design and technological parameters of an experimental sample of the color sorter, carried out within the framework of the grant project of the Ministry of Education and Science of the Republic of Kazakhstan AP05130398. The regularities of the technological process of color sorting - cleaning of clover seeds from seeds of quarantine and hardseparable impurities and rational regimes providing high efficiency of processing of clover seed material - have been established. A constructive feature of the tray feeding the seed mixture is proposed, which allows reducing the massiveness of the separator while increasing the productivity, reducing the useful production area.