Abstract

Seed pods of oilseed rape (Brassica napus) are fragile at harvest maturity and seed loss can be a significant fraction of potential yield if bad weather occurs when the crop is most vulnerable. Even in good weather, loss of up to 25% has been reported when harvest operations are late. Plant breeders need to be able to identify accurately single plants that provide resistance to pod shatter from amongst very large breeding populations. A ‘random impact’ test, involving controlled agitation of samples of 20 pods to measure their breaking response, was used to compare 12 experimental lines, to fit a model and hence to estimate the sample half-lives found to range from 2·6 to 129 s. Using the fitted model, the treatment time for any fraction opened could then be estimated. For cultivar Apex to reach 25% of pods opened, equivalent to reported seed loss caused by bad weather in standing crops, the treatment time was found to be 17 s, with fiducial limits of 12 and 22 s. The 11% loss reported in field crops in normal conditions was achieved at 9·7 s agitation time, with fiducial limits of 5·1 and 14 s. The fraction of pods opened at 17 s for the other 11 lines was then estimated from the model. In two lines, less than 10% of pods opened, suggesting that these pods have a much better potential to survive intact than pods of current cultivars. The methodology proposed is potentially of value in oilseed rape breeding.

The silique shattering resistance index (SSRI) of 229 accessions (Brassica napus L.) was investigated through random impact test (RIT) for screening silique shattering (SS) resistance. The accessions displayed wide variation in SSRI, which ranged from 0.000 to 0.7675 with the variance coefficient (CV) of 114.4%. Only two varieties (accounting for 0.9%) showed SS resistance; about 3.93% of the varieties (lines) showed relative resistance to SS; and about 8.73% were identified as the medium. Most (59.38%) of the varieties (lines) were identified as very susceptible germplasm to SS, and 27.07% as the susceptible germplasm. According to independent experiments in three years with 6 representative varieties (lines), the SSRI was dominated by genetic factor with obvious interactions with environment, and the RIT showed stable results within years. The simple correlation analysis showed that the SSRI had significant (P<0.01) negative correlation with silique number per centimeter, and significant (P<0.01) positive correlations with silique wall thickness, silique length, silique width, beak length, and seed number per silique. However, the correlation coefficients (CV) were rather small indicating the selection potential of varieties with high SSRI and fine silique traits via recombination in B. napus breeding programs.

利用随机碰撞测试方法, 对229份自交纯合的甘蓝型油菜品种(系)进行了抗裂角指数测定, 以期筛选出抗裂角种质。结果表明, 抗裂角性状在现有品种(系)中存在广泛变异, 变异系数达114.4%。发现了2份抗裂角的品种(系), 占0.9%; 较抗的资源占3.93%; 处于中间状态的品种(系)占8.73%; 易裂角资源占27.07%, 极易裂角的品种(系)占59.39%。选择6个品种(系)进行了连续3年的测试, 表明抗裂角性状由品种(系)的遗传特性决定, 但受环境条件影响; 随机碰撞法具有较好的重现性。简单相关分析显示, 抗裂角指数与角果密度呈显著负相关, 与角皮厚度、角果长度、角果宽度、角喙长度、角粒数呈显著正相关, 但相关系数都很小。

Silique shatter strength (SSS) of 286 Brassica napus varieties (lines) was measured using a modified fracture method. Results indicated a wide variation in silique shattering resistance among these accessions. Among 146 hybrid varieties’ SSS values, 3 (2.05%) were less than 1N, 96 (65.75%) were between 1 to 2N, 47 (32.19%) were between 2 to 3N, no hybrid was found having more than 3N of SSS. The SSS of hybrids ranged between 0.82 to 2.87N, with an average of 1.83N, and CV (coefficient of variation) of 22.11%. Among 140 conventional varieties, 6 (4.29%) were less than 1N, 76 (54.29%) were between 1 to 2N, 49 (35%) were between 2 to 3N, and 9 (6.42%) were more than 3N. The SSS of conventional varieties ranged between 0.58 to 3.47N, with an average of 1.94N, and CV of 31.55. Correlations between SSS and silique- and seed-related traits showed that the SSS had highly significant positive correlations with single silique weight, unit area weight of silique wall, and 1 000-seed weight. And it had significant positive correlations with seed per silique and silique width. Analysis of the relations between hybrids and its restorers illustrated that the hybrid SSS had significant positive correlations with silique width, single silique weight, unit area weight of silique wall, and 1 000-seed weight of the restorer. Results indicated that silique size affected shattering trait. Rapeseed with large silique, thick wall and heavy seeds might have higher resistance to silique shattering. And large silique and heavy seeds of restorer lines would provide greater benefit to the shattering resistance of hybrids.

应用改良拉裂法，对286份甘蓝型油菜品种(系)进行裂角力测定。结果表明，抗裂角性状在现有甘蓝型油菜品种(系)中存在广泛变异。在146份甘蓝型杂交油菜品种（组合）中，裂角力变异范围0.82～2.87N（牛顿），平均裂角力1.83N，变异系数22.11%；裂角力小于1N的有3份（占2.05%），在1～2N之间的96份（占65.75%），在2～3N之间的47份(占32.19%)，没有检测到裂角力大于3N的品种或组合。在140份甘蓝型常规油菜品种（系）中，裂角力变异范围0.58～3.47N，平均裂角力1.94N，变异系数31.55%，均高于杂交油菜，其中裂角力小于1N的6份(占4.29%)，在1～2N之间的76份(占54.29%)，在2～3N之间的49份(占35%)，大于3N的9份(占6.42%)。与角果和籽粒性状的相关分析表明，油菜角果的裂角力值与单角壳重、单位面积壳重、千粒重达极显著正相关，与每角粒数和角果宽度达到显著正相关。分析杂种与亲本恢复系之间的关系，发现杂种裂角力与恢复系的角果宽度、单角壳重、单位面积壳重、千粒重等性状呈极显著正相关，与粒壳比呈极显著负相关。说明角果大小显著影响油菜的抗裂角特性，角果大、果壳厚、千粒重高等可以作为筛选抗裂角油菜的形态指标。在杂交油菜育种中选用大角大粒恢复系亲本能有效提高杂交油菜的抗耐裂角性。