División de Ciencias Ambientales, Instituto Potosino de Investigación Científica y Tecnológica, San Luis Potosí, S.L.P., México.
Plant Biol (Stuttg). 2011 Jan;13(1):154-9. doi: 10.1111/j.1438-8677.2010.00333.x.
Seeds of Opuntia spp. have physiological dormancy; they need a period of after-ripening to break dormancy, and the embryos have low growth potential. We evaluated the combined effects of seed age and presence of fungi on the testa on germination of Opuntia streptacantha, an abundant species in the Chihuahuan Desert (Mexico), assuming that older seeds have broken seed dormancy and fungi can reduce mechanical resistance to germination. In a preliminary experiment, we found no germination of 9-year-old (1998) and freshly collected (2007) seeds. However, we obtained 67% and 27% germination from 9-year-old and fresh non-sterilized seeds, respectively, and found fungi growing on the testa of all germinated seeds. Two fungal strains were isolated and identified using ribosomal internal transcribed spacer (ITS) sequence analysis: Penicillium chrysogenum and Phoma sp. In a second experiment, we inoculated seeds with strains of P. chrysogenum and Phoma sp., as well as Trichoderma koningii and binucleate Rhizoctonia (Gto17S2), to evaluate their ability to break seed dormancy. Seeds inoculated with P. chrysogenum, Phoma sp. and T. koningii had higher germination than controls for both seed ages, but germination was higher in older seeds. Scanning electron microscopy showed that these fungi eroded the funiculus, reducing its resistance. Binucleate Rhizoctonia did not lead to germination and controls had almost no germination. Our results strongly indicate that fungi are involved in breaking seed dormancy of O. streptacantha, and that the effect of fungi on seeds is species-specific.
仙人掌属的种子具有生理休眠性；它们需要经过后熟期才能打破休眠，而且胚胎的生长潜力较低。我们评估了种子年龄和真菌存在对果皮对奇瓦瓦沙漠（墨西哥）丰富物种刺梨发芽的综合影响，假设较老的种子已经打破了种子休眠，真菌可以降低发芽的机械阻力。在初步实验中，我们发现 9 年（1998 年）和新鲜采集（2007 年）的种子均未发芽。然而，我们从 9 年的非灭菌种子和新鲜种子中分别获得了 67%和 27%的发芽率，并且发现所有发芽种子的果皮上都有真菌生长。使用核糖体内部转录间隔区（ITS）序列分析，我们从这些种子上分离并鉴定出两种真菌菌株：产黄青霉和茎点霉。在第二个实验中，我们用产黄青霉、茎点霉和哈茨木霉以及双核立枯丝核菌（Gto17S2）菌株接种种子，以评估它们打破种子休眠的能力。与对照相比，用产黄青霉、茎点霉和哈茨木霉接种的种子在两个种子年龄阶段的发芽率都更高，但在较老的种子中发芽率更高。扫描电子显微镜显示，这些真菌侵蚀了种脐，降低了其阻力。双核立枯丝核菌没有导致发芽，对照几乎没有发芽。我们的结果强烈表明，真菌参与了打破刺梨种子的休眠，并且真菌对种子的作用是特异性的。
