Orellana-Torrejon Carolina, Vidal Tiphaine, Gazeau Gwilherm, Boixel Anne-Lise, Gélisse Sandrine, Lageyre Jérôme, Saint-Jean Sébastien, Suffert Frédéric
Université Paris-Saclay, INRAE, UR BIOGER, 91120 Palaiseau, France; Université Paris-Saclay, INRAE, AgroParisTech, UMR ECOSYS, 91120 Palaiseau, France.
Université Paris-Saclay, INRAE, UR BIOGER, 91120 Palaiseau, France.
Fungal Genet Biol. 2022 Nov;163:103744. doi: 10.1016/j.fgb.2022.103744. Epub 2022 Oct 7.
Little is known about the impact of host immunity on sexual reproduction in fungal pathogens. In particular, it is unclear whether crossing requires both sexual partners to infect living plant tissues. We addressed this issue in a three-year experiment investigating different scenarios of Zymoseptoria tritici crosses according to the virulence ('vir') or avirulence ('avr') of the parents against a qualitative resistance gene. Co-inoculations ('vir × vir', 'avr × vir', 'avr × avr') and single inoculations were performed on a wheat cultivar carrying the Stb16q resistance gene (Cellule) and a susceptible cultivar (Apache), in the greenhouse. We assessed the intensity of asexual reproduction by scoring disease severity, and the intensity of sexual reproduction by counting the ascospores discharged from wheat residues. As expected, disease severity was more intense on Cellule for 'vir × vir' co-inoculations than for 'avr × vir' co-inoculations, with no disease for 'avr × avr'. However, all types of co-inoculation yielded sexual offspring, whether or not the parental strains caused plant symptoms. Parenthood was confirmed by genotyping (SSR markers), and the occurrence of crosses between (co-)inoculated and exogenous strains (other strains from the experiment, or from far away) was determined. We showed that symptomatic asexual infection was not required for a strain to participate in sexual reproduction, and deduced from this result that avirulent strains could be maintained asymptomatically "on" or "in" leaf tissues of plants carrying the corresponding resistant gene for long enough to reproduce sexually. In two of the three years, the intensity of sexual reproduction did not differ between the three types of co-inoculation in Cellule, suggesting that crosses involving avirulent strains are not anecdotal. We discuss the possible mechanisms explaining the maintenance of avirulence in Z. tritici populations and the potential impact of particular resistance deployments such as cultivar mixtures for limiting resistance breakdown.
关于宿主免疫对真菌病原体有性繁殖的影响，人们了解甚少。特别是，尚不清楚杂交是否要求两个性伴侣都感染活的植物组织。我们在一项为期三年的实验中解决了这个问题，该实验根据亲本对一个定性抗性基因的毒性（“vir”）或无毒性（“avr”），研究了小麦壳针孢杂交的不同情况。在温室中，对携带Stb16q抗性基因的小麦品种（Cellule）和一个感病品种（Apache）进行了共接种（“vir×vir”、“avr×vir”、“avr×avr”）和单接种。我们通过对病害严重程度评分来评估无性繁殖的强度，通过计算从小麦残体中释放的子囊孢子数量来评估有性繁殖的强度。正如预期的那样，“vir×vir”共接种在Cellule上的病害严重程度比“avr×vir”共接种更严重，“avr×avr”则无病害。然而，所有类型的共接种都产生了有性后代，无论亲本菌株是否引起植物症状。通过基因分型（SSR标记）确认了亲本关系，并确定了（共）接种菌株与外源菌株（实验中的其他菌株或来自远方的菌株）之间杂交的发生情况。我们表明，菌株参与有性繁殖不需要有症状的无性感染，并从这一结果推断，无毒菌株可以在携带相应抗性基因的植物叶片组织上或组织内无症状地维持足够长的时间以进行有性繁殖。在三年中的两年里，Cellule中三种共接种类型的有性繁殖强度没有差异，这表明涉及无毒菌株的杂交并非罕见。我们讨论了解释小麦壳针孢群体中无毒性状维持的可能机制，以及特定抗性部署（如品种混合）对限制抗性丧失的潜在影响。
