Zheyouza 59, a rapeseed variety with superior resistance and excellent yield

Dear Editor:

Rapeseed (Brassica napus L.) is one of the most important oil crops worldwide. Its yield, quality, and adaptation have been key breeding targets in recent decades. Particular examples of the targets are silique dehiscence which causes harvest loss, as well as sclerotinia stem rot and clubroot which are major determinants of losses among live plants.

Rapeseed siliques dehisce easily causing heavy losses. This inhibits mechanized harvesting and restricts further improvements of production efficiency (Kuai et al. 2016). It is reported from worldwide commercial rapeseed production data that silique dehiscence (silique shattering) can cause 8%–12% pre-harvest losses, with up to 50% lost in adverse weather conditions (Jaradat et al. 2014). Silique shattering characteristics have been chosen as an essential evaluation indicator of rapeseed, especially for mechanical harvesting. Shattering tests for Chinese winter rapeseed varieties organized by the Oil Crops Research Institute, Chinese Academy of Agricultural Sciences show that, up to now, most varieties have been defined as “highly shattering” (shattering resistance index, SRI ≤ 0.20) or “shattering” (0.2 < SRI ≤ 0.40), with only a smaller proportion showing “low shattering resistance” (0.40 < SRI ≤ 0.60).

Sclerotinia stem rot and clubroot are two of the primary diseases in rapeseed caused by Sclerotinia sclerotiorum and Plasmodiophora brassicae, respectively. Sclerotinia stem rot causes the necrosis of stems and leaves and can result in up to 80% yield loss. Currently, only a few varieties with partial resistance to S. sclerotiorum have been reported; highly or completely resistant lines of rapeseed are not available (Ding et al. 2021). The lack of a resistant source has greatly restrained the resistance breeding of B. napus. Clubroot has been spreading rapidly worldwide and has been found in more than 60 countries (Chai et al. 2014), resulting in remarkably decreased (20%–90%) yields (Wang et al. 2012). The clubroot spores can survive up to 20 years in soil (Donald and Porter 2009; Kageyama and Asano 2009), making it difficult to manage by chemical, cultural and biological practices once the soil is contaminated. Non-resistance to clubroot has been identified in most rapeseed varieties.

In recent years, greater global demand for rapeseed has led to intensified cultivation practices, increasing the urgency for effective strategies against losses from silique shattering, S. sclerotiorum and P. brassicae. In response, we have been carrying out a rapeseed multi-resistance breeding program. Zheyouza 59 (ZYZ59) was an elite cultivar with a superior agronomic performance and high yield. It has relatively high resistance to biotic stress from S. sclerotiorum and P. brassicae, as well as to silique dehiscence Fig. 1.

Fig. 1.

Growth stages and approval of ZYZ59 as a new rapeseed variety. a–e. flower, leaf, silique, seedling and whole plant of ZYZ59; f. field performance of ZYZ59 in Haining in 2023; g. approval certificate by Ministry of Agriculture and Rural Affairs of the People’s Republic of China

ZYZ59 is a hybrid cultivar derived from the genic male sterility (GMS) line (9012A) system, and bred by crossing ZH3A × HR59. ZH3A is the female parent and HR59 the male parent. ZH3A is a recessive genic male sterile line bred from the offspring of the cross Wanyou 18 (WY18) × Xiangzayou 5 (XZY5). ZH3A was developed in 2013 and certified by the Zhejiang provincial crop variety certification committee (Fig S1). The male parental line (HR59) is an elite restorer line with superior clubroot and silique dehiscence resistance, derived by continuous selection from the offspring of the cross Xiangzayou 5 (XZY5) × Zhongshuang 11 (ZS11).

The breeding pedigree of ZYZ59 is shown in Fig S2. In the spring of 2017, the ZH3A × HR59 cross was carried out in the experimental farm of Zhejiang Academy of Agricultural Sciences, Hangzhou, China. In 2017 and 2018, the F₁ hybrid was entered into the regional rapeseed varietal test in the middle reaches of the Yangtze River. Trial planting was organized by the Oil Crops Research Institute, Chinese Academy of Agricultural Sciences, and took place in ten areas from four provinces (Hubei, Hunan, Jiangxi and Henan). In 2018 and 2019 the F₁ hybrid was entered into in the regional rapeseed varietal test in the lower reaches of Yangtze River. Here, the ten planting areas were in Jiangsu, Zhejiang, Anhui and Shanghai. In all these trials, yield, quality, disease resistance and silique shattering resistance were evaluated and compared between varieties (Table S1, Table S2, Table S3, Table S4).

In the regional rapeseed varietal tests of the middle and lower reaches of Yangtze River, ZYZ59 yielded 175.00–182.72 kg/667 m² and 188.33–203.41 kg/667 m² in the two test regions, showing increased yield production compared with the control variety in all these trials. The whole growth duration of ZYZ59 was 203.6–213.7 days in the middle reaches of Yangtze River and 217.9–223.5 days in the lower reaches of Yangtze River, which was similar with the control variety Huayouza 12 and Qinyou 10. ZYZ59 showed plant height of 173.0–175.2 cm and 175.6–181.1 cm, branch number of 6.4–6.5, silique number of 228–392.7, seed number per silique of 19.9–20.6, seed weight of 3.87–4.51 g and oil content of 45.95%–46.88% (Table S5, Table S6). In summary, the agronomic traits of ZYZ59 were excellent. Better performance of yield and yield-related traits were observed in the lower reaches of Yangtze River compared with the middle reaches, but whole growth duration was shorter in the middle reaches of Yangtze River for this cultivar.

During the harvest season of 2018, ZYZ59 was included in a silique shattering test organized in the Yangluo experimental farm by Oil Crops Research Institute, Chinese Academy of Agricultural Sciences. ZYZ59 showed the highest silique shattering resistance among the 36 test varieties from the regional rapeseed varietal test of lower reaches of Yangtze River, with SRI as high as 0.6733. ZYZ59 was defined as moderately resistant to silique shattering in this test.

The Sclerotinia sclerotiorum resistance of ZYZ59 was evaluated in the two regional tests (Table S5, Table S6), ranging between light to moderate resistance levels, with resistance indexes of 8.71–8.88 and 10.37–14.17.

The clubroot resistance of the parental line HR59 and the hybrid cultivar ZYZ59 was measured and certified by Shenyang Agricultural University (Table S7). HR59 showed resistance to two pathotypes (Pb2 and Pb4) of P. brassicae, with individual disease incidence recorded as 19.4% and 0.0%, as well as disease indexes of 14.8 and 0.0, respectively. A certain clubroot resistance was also observed in ZYZ59 against the Pb2 pathotype of P. brassicae.

Supplementary Information

Below is the link to the electronic supplementary material.

Author contributions

Ying Fu completed the field work of the breeding. Huasheng Yu put forward the concept of resistance cultivar breeding and designed the breeding program. Quanfeng Zhang, Huabing Lu, and Daomin Liu participated in varietal evaluation. Yaofeng Zhang assisted with the data investigation.

Funding

This research was supported by the Project of Zhejiang Provincial Natural Science Foundation of China (Grant No. LY23C130007) and the Project of National Biological Breeding (Grant No. 2023ZD04042).

Data availability

The data supporting the results reported in the article is available in supplementary material.

Declarations

Conflict of interest

The authors have no relevant financial or non-financial interests to disclose.