Plant traits associated with resistance to Thrips tabaci in cabbage (Brassica oleracea var capitata)

Thrips tabaci is a major problem in the cultivation of cabbage for storage, as this pest causes symptoms that necessitate the removal of affected leaves from the product. Between cabbage varieties large differences in susceptibility occur. This study aimed to identify plant traits associated with these differences, in field experiments with natural infestation in 2005 and 2006. One factor affecting the amount of thrips damage was the timing of the development of the head. In an experiment with different planting dates especially the early maturing, more susceptible varieties were shown to benefit from later planting. In comparisons of multiple varieties in both years, regression studies showed that more advanced plant development in August and early September increased thrips damage at the final harvest. However, no single plant trait explained more than 25% (2005, Brix) or 48% (2006, compactness) of the variation in thrips damage. Optimal regression models, explaining up to 75% of the variation in thrips damage included Brix and leaf surface wax late in the season, as well as an indicator of plant development earlier in the season, and in 2005 also leaf thickness. The possible role of these plant traits in relation to thrips is discusse

Earliness, leaf surface wax and sugar content predict varietal differences for thrips damage in cabbage

When cabbage is cultivated for storage in the Netherlands, it is usually harvested around mid-October. This type of cabbage crop may be severely damaged by thrips (Thrips tabaci). The thrips population on the plants and the more severe symptoms develop mostly during September and October. Also during cold storage symptoms continue to develop. The damage caused by thrips is due to the symptoms that develop after feeding, which are small callus-like growths that will turn brownish after some time and which may cover substantial amounts of leaf area. Large differences exist between cabbage varieties in their susceptibility to thrips damage. It is not clear whether these differences are due to resistance (affecting the thrips population in the plant) or to tolerance (affecting the development of symptoms upon thrips feeding). Further, not much is known about plant traits affecting the resistance or tolerance to thrips. In order to guide selection and breeding for resistance to thrips, this study aimed to identify plant traits causing these differences. In the years 2005, 2006 and 2007 we performed field experiments with collections of varieties differing in a number of plant traits, with earliness varying from moderately late to very late. In the field experiments we relied upon natural infestation by thrips. Several times during the period August-October plants were harvested and assessed for the amount of thrips damage and the number of thrips, as well as for several morphological and physiological traits, including head circumference, leaf thickness, developmental stage, head compactness, leaf surface wax, and Brix value as an indication of the content of soluble sugars. One factor affecting the amount of thrips damage was the timing of the development of the head. Regression studies showed that more advanced plant development at the end of August increased thrips damage at the final harvest. Other plant traits affecting thrips damage were Brix and the amount of leaf surface wax. However no single plant trait explained more than 45% of the variation in thrips damage at the final harvest. Optimal regression models, explaining up to 75% of the variation in thrips damage included Brix and leaf surface wax late in the season, as well as an indicator of plant development earlier in the season, and in 2005 also leaf thickness. The possible role of these plant traits in relation to thrips is discussed

The organic seed regulations framework in Europe – current status and recommendations for future development

Organic agriculture regulations, in particular European regulation EC 889/2008, prescribe the use of organically produced seed. For many cultivated plants, however, organic seed is often not available. This is mainly because investment in organic plant breeding and seed production has been low in the past. To bridge the gap between organic seed supply and demand, national and European regulations define certain circumstances under which organic producers are permitted to use non-organically produced seed. While the organic sector currently depends on these concessions, they also threaten to impede a further increase in the demand for organic seed, thereby potentially restraining present and future investment in organic seed production and plant breeding. We review the current status of the organic seed regulations framework by analysing key issues such as the role of the national derogation regimes, the role of expert groups, databases and seed prices. Key points are that (a) the situation of the organic seed sector has improved over the last few years; however, (b) reporting on organic seed to the EU by different countries needs to be harmonised; (c) the success of the organic seed sector depends critically on the implementation and improvement of national expert groups; and (d) to protect genetic diversity, the use of local varieties and landraces should not be impeded by organic seed regulations

Participatory plant breeding: a way to arrive at better-adapted onion varieties

The search for varieties that are better adapted to organic farming is a current topic in the organic sector. Breeding programmes specific for organic agriculture should solve this problem. Collaborating with organic farmers in such programmes, particularly in the selection process, can potentially result in varieties better adapted to their needs. Here, we assume that organic farmers' perceptive of plant health is broader than that of conventional breeders. Two organic onion farmers and one conventional onion breeder were monitored in their selection activities in 2004 and 2005 in order to verify whether and in which way this broader view on plant health contributes to improvement of organic varieties. They made selections by positive mass selection in three segregating populations under organic conditions. The monitoring showed that the organic farmers selected in the field for earliness and downy mildew and after storage for bulb characteristics. The conventional breeder selected only after storage. Farmers and breeder applied identical selection directions for bulb traits as a round shape, better hardness and skin firmness. This resulted in smaller bulbs in the breeders’ populations, while the bulbs in the farmer populations were bigger than in the original population. In 2006 and 2007 the new onion populations will be compared with each other and the original populations to determine the selection response

BIO-IMPULS: innovatie in de biologische aardappelketen

In 2008 is het project BIO-IMPULS gestart om de biologische aardappelteelt in Nederland te verbeteren. BIO-IMPULS richt zich op innovaties in de gehele aardappelketen, van veredeling, teeltoptimalisatie (gewasbescherming, teeltvervroeging, bemesting, oogst en bewaring) en de markintroductie van nieuwe rassen en producten tot voorlichting en kennisoverdrach

Passen moleculaire merkers bij de zoektocht naar biologische rassen? : Internationale discussie legt praktische en principiële bezwaren bloot

Bespreking van de voor- en nadelen van 'merkergestuurde selectie' bij veredelingsonderzoek in de biologische landbou

Perspectieven voor veredeling op stikstofefficiëntie bij sluitkool (Literatuuroverzicht)

Kool is een belangrijk gewas in Nederland. Koolsoorten vragen veel stikstof (ca. 300 kg N/ha)voor een goede groei, dikwijls meer dan binnen de huidige regelgeving in een biologische vruchtwisseling kan worden geleverd. Stikstof verhoogt de opbrengst, maar bij een hoog stikstofaanbod bereikt de opbrengst een plafond. Er is in het verleden veel onderzoek gedaan om de bemesting te optimaliseren. Voor een verdere verduurzaming van de teelt is het de vraag welke rassen robuust genoeg zijn om bij een beperkte hoeveelheid stikstof en wisselende weers- en groeiomstandigheden toch een economisch acceptabele en stabiele opbrengst te geven. En welke planteigenschappen spelen daarbij een cruciale rol? Door middel van literatuuronderzoek, gesprekken met deskundigen en veldbezoeken is nagegaan wat de perspectieven zijn om te veredelen op stikstofefficiëntie bij koolsoorten, met name bij sluitkool. Stikstofefficiëntie is de resultante van twee componenten: stikstofopname-efficiëntie en stikstofgebruiksefficiëntie. Deze aspecten moeten steeds in onderlinge relatie onderzocht worden, omdat rassen diverse combinaties van strategieën kunnen ontwikkelen om efficiënt met een laag stikstofaanbod om te kunnen gaan. Weliswaar is het meeste onderzoek naar stikstofefficiëntie bij Brassica gewassen gedaan aan koolzaad, Chinese kool en bloemkool, maar uit dit voorliggende onderzoek zijn goede aanknopingspunten gevonden voor verbetering van stikstofefficiëntie bij sluitkool. Voor de opname van stikstof is goede beworteling een voorwaarde. Kool blijkt diep te kunnen wortelen en efficiënt stikstof uit de bodem te kunnen opnemen. Er is echter nog geen onderzoek gedaan naar mogelijke rasverschillen in beworteling (diepte, intensiteit, en plasticiteit) bij sluitkool onder een laag stikstofaanbod. Omdat in de biologische teelt stikstof bij koude minder makkelijk beschikbaar komt, is het belangrijk om in bewortelingsonderzoek vooral ook vroege rassen te betrekken. Daarbij is het tevens van belang diverse locaties in het onderzoek te betrekken omdat verschillen in beworteling niet onder alle omstandigheden tot expressie komen. Uit de literatuur valt af te leiden dat voor kool vooral winst te behalen is bij het verbeteren van de gebruiksefficiëntie. Daarbij lijkt het van belang dat het omblad zo lang mogelijk, tot aan de oogst, actief blijft teneinde de stikstofopname te stimuleren. Ook de herverdeling van stikstof van het oude blad naar het jonge (binnen)blad dat de kool vormt en dat niet fotosynthetisch actief kan zijn, is belangrijk. Deze gebruiksprocessen en de verhouding tussen omblad en jong blad en daarmee samenhangende gebruiksprocessen kunnen verschillen voor vroege, middelvroege en late rassen. Nader onderzoek moet uitwijzen wat de ideale verhouding van omblad en kool (harvest index) is in relatie tot stikstofefficiëntie, en of bladstand en bladopbouw daarbij een rol spelen. Daarbij zou het interessant kunnen zijn te onderzoeken of ook andere selectiecriteria van belang kunnen zijn, zoals de bebladeringsindex (bladoppervlak/grondoppervlak, m2/m2), specifiek bladoppervlak (bladoppervlak/bladgewicht, cm2/g), nitraatreductase en / of chlorofylgehalte of -fluorescentie

Caby Photometry of the Hyades: Comparisons to the Field Stars

Intermediate-band photometry of the Hyades cluster on the Caby system is presented for dwarf stars ranging from spectral type A through late K. A mean hk, b-y relation is constructed using only single stars without anomalous atmospheres and compared to the field stars of the solar neighborhood. For the F dwarfs, the Hyades relation defines an approximate LOWER bound in the two-color diagram, consistent with an [Fe/H] between +0.10 and +0.15. These index-color diagrams follow the common convention of presenting stars with highest abundance at the bottom of the plot although the index values for the metal-rich stars are numerically larger. For field F dwarfs in the range [Fe/H] between +0.4 and -1.0, [Fe/H] = -5.6 delta-hk + 0.125, with no evidence for a color dependence in the slope. For the G and K dwarfs, the Hyades mean relation crosses the field star distribution in the two-color diagram, defining an approximate UPPER bound for the local disk stars. Stars found above the Hyades stars fall in at least one of three categories: [Fe/H] below -0.7, [Fe/H] above that of the Hyades, or chromospherically active. It is concluded that, contrary to the predictions of model atmospheres, the hk index for cool dwarfs at a given color hits a maximum value for stars below solar composition and, with increasing [Fe/H] above some critical value, declines. This trend is consistent, however, with the predictions from synthetic indices based upon much narrower Ca filters where the crossover is caused by the metallicity sensitivity of b-y.Comment: 13 pages, 9 eps figures, 1 tex table, 1 ascii tabl

Are specific testing protocols required for organic onion varieties? Analysis of onion variety testing under conventional and organic growing conditions

Organic growers need information on variety performance under their growing conditions. A 4-year onion variety research project was carried out to investigate whether setting up a variety testing system combining conventional and organic variety trials is feasible and efficient rather than organizing separate variety trials under the two management systems. During 4 years commercial onion cultivars were tested at a certified organic and a non-organic location. Both systems were managed without chemical pest, disease and sprouting control, but differed in fertility management (organic manure in autumn versus synthetic fertilizer), soil cultivation and weed management (mechanical weeding versus application of herbicide). Management system significantly affected plant density, thickness of neck, and proportion of small and large bulbs. Variety × management system interactions were significant for bulb uniformity, earliness, proportion of large bulbs, dormancy and relative storage success but did not change the ranking of the varieties. We conclude that organic growers can profit from a more conscious variety choice when conventionally fertilised trials would refrain from using pesticides, fungicides, herbicides and sprout inhibitors. However, this would require an adaptation of the management protocol in such a way that trials might no longer represent conditions of conventional farmers. Furthermore, assessments of leaf erectness, disease resistance to downy mildew and leaf blight should be included in the protocols for organic use. We advocate better communication between breeders and growers on specific variety characteristics contributing to improving yield stability under low-input, organic growing condition