Oilseed rape (Brassica napus) as a resource for farmland insect pollinators: quantifying floral traits in conventional varieties and breeding systems

Abstract

Oilseed rape (OSR; Brassica napus L.) is a major crop in temperate regions and provides an important source of nutrition to many of the yield‐enhancing insect flower visitors that consume floral nectar. The manipulation of mechanisms that control various crop plant traits for the benefit of pollinators has been suggested in the bid to increase food security, but little is known about inherent floral trait expression in contemporary OSR varieties or the breeding systems used in OSR breeding programmes. We studied a range of floral traits in glasshouse‐grown, certified conventional varieties of winter OSR to test for variation among and within breeding systems. We measured 24‐h nectar secretion rate, amount, concentration and ratio of nectar sugars per flower, and sizes and number of flowers produced per plant from 24 varieties of OSR representing open‐pollinated (OP), genic male sterility (GMS) hybrid and cytoplasmic male sterility (CMS) hybrid breeding systems. Sugar concentration was consistent among and within the breeding systems; however, GMS hybrids produced more nectar and more sugar per flower than CMS hybrid or OP varieties. With the exception of ratio of fructose/glucose in OP varieties, we found that nectar traits were consistent within all the breeding systems. When scaled, GMS hybrids produced 1.73 times more nectar resource per plant than OP varieties. Nectar production and amount of nectar sugar in OSR plants were independent of number and size of flowers. Our data show that floral traits of glasshouse‐grown OSR differed among breeding systems, suggesting that manipulation and enhancement of nectar rewards for insect flower visitors, including pollinators, could be included in future OSR breeding programmes.

An analysis of the energetic reward offered by field bean (Vicia faba) flowers: Nectar, pollen, and operative force

“…Bees may then preferentially visit fields of optimized varieties over less rewarding flowers in the environment, based on location cues. Similar possibilities for nectar production have also recently been shown in two other pollinator-dependent crops-sunflower and oilseed rape (Carruthers et al, 2017;Mallinger & Prasifka, 2017). We suggest for V. faba that this could be achieved most effectively by improving the pollen production and nectar sugar concentration of flowers (but not above 55% w/w), while maintaining an average volume of nectar in flowers.…”

“…Therefore, optimal floral trait combinations to attract pollinators and maintain high pollination rates may have been lost by genetic drift or selective sweeps. This has led to the suggestion that breeding crops through selecting for floral traits could lead to improvements in food security by attracting greater numbers of pollinators, as well as improving foraging resources for wild pollinator communities (e.g., Bailes, Ollerton, Pattrick, & Glover, 2015;Carruthers et al, 2017;Mallinger & Prasifka, 2017;Palmer, Perez, Ortiz-Perez, Maalouf, & Suso, 2009).…”

The potential of crop management practices to reduce pollen beetle damage in oilseed rape

“…The optimum pod number for maximum OSR yield is in the region of 6000-8000 pods/m 2 (Berry and Spink 2006). However, significantly more flowers than necessary for optimum pod number are usually produced, and the presence of these 'excess flowers' enables the crop to tolerate some pollen beetle-related flower loss before yields are reduced (Ellis and Berry 2012); excess flower numbers have been shown to vary according to cultivar (Ellis and Berry 2012;Carruthers et al 2017) and thus are likely to be important determinant of a particular cultivar's tolerance to pollen beetle attack. A recent study showed that, in general, cultivars bred using the cytoplasmic male-sterility (CMS) technique generally had more flowers than hybrids produced by genetic male-sterility (GMS) techniques and open-pollinated varieties (Carruthers et al 2017).…”

Heterogeneous Distribution of Erucic Acid in Brassica napus Seeds

“…Brassica napus (AACC, 2n = 38) is an allotetraploid oilseed plant species formed by the hybridization of two diploid species of Brassica rapa (AA,2n = 20) and Brassica oleracea (CC, 2n = 18) about 7,500 years ago (Chalhoub et al, 2014;An et al, 2019). It is the third largest oil crop in the world and accounts for approximately 15% of the vegetable oil used for human consumption (Wells et al, 2014;Liu et al, 2016;Carruthers et al, 2017;Kaur et al, 2019). Like most oilseeds, triacylglycerols (TAGs) comprise 95% of B. napus seed oil which are composed of a glycerol backbone esterified with three fatty acyl chains (Ai et al, 2014;Guan et al, 2016).…”