Apetalous canola (Brassica napus) hybrid seed production

Canola has become an important crop in Australia as demand for its oil continues to increase and the benefits of including it in cropping rotations are recognised. During flowering canola produces an inefficient crop canopy of bright yellow flowers, which reduces radiation penetration. This results in increased leaf senescence and slower crop growth during this stage of development. In an attempt to alleviate this effect the apetalous characteristic (absence of flower petals) was introduced into breeding lines, and incorporated into a cytoplasmic male sterility (CMS) system. The ogura CMS used was a newly developed system which had been introduced from radish (Raphanus sativus) . This study investigated the yields obtained from apetalous male sterile canola lines, in order to determine if apetalous hybrid seed can be produced commercially. Over three years of field trials the yields obtained from apetalous male sterile lines were significantly lower than those of a male sterile petalled line also containing the ogura CMS. The low yields were attributed to the apetalous male sterile lines setting a low percentage of pods from potential pod sites, and very few seeds/pod. Apetalous male sterile plants showed a strong response to hand pollination, by setting more pods and seeds/pod than plants which were not artificially pollinated, while there was no effect seen in the petalled control. This implied that the apetalous male sterile plants were not being adequately pollinated in the field by insect vectors, which in this study was primarily honey bees. Observations made in the field of bee numbers and behaviour showed that the apetalous lines attracted a similar number of bees as the petalled line, however a high percentage of apetalous flowers were 'side-worked' and therefore unlikely to be pollinated. Pollen transfer experiments conducted in the glasshouse investigated the effect of bees side-working flowers and showed that the amount of pollen deposited on apetalous male sterile flowers was 60% lower than on flowers with petals, this appeared to be the major reason that apetalous flowers produced fewer seeds/pod. Both the apetalous and petalled male sterile lines were found to produce fewer seeds/m2 from each row the further it was situated from the pollen source. Logarithmic regression equations were calculated which were able to explain a large proportion of the variation in the number of seeds/m2 between rows. It was proposed that these regression models could be useful in determining A:R line ratios for hybrid seed production blocks.