The most widely used apple rootstock Malling-Merton 106 is highly susceptible to collar rot disease caused by Phytophthora cactorum. In the present study, in vitro selection method was employed for early screening of collar rot tolerance among regenerants of MM106. Toxic filtrates produced by three virulent isolates of P. cactorum were mixed and tested as a selection agent. Adventitious shoots were regenerated from leaf explants of MM106, cloned and exposed to proliferation MS medium enriched with 20–80% (v/v) of pathogen culture filtrate to isolate tolerant regenerants. Varying concentrations of culture filtrate resulted in browning, necrosis and reduced growth which led to the identification of tolerant shoots.The survived tolerant regenerants were subjected to three continuous and one discontinuous selection cycle. The critical concentration of culture filtrate was found to be 74%, resulting in 37.8% survival of regenerated shoots after becoming necrotic. Regenerants selected on 70%, 72% and 74% culture filtrate enriched medium showed 52%, 50% and 33.3%, survival respectively after 2nd selection cycle, while reduced to 87%, 81% and 0 respectively after 3rd selection cycle. In discontinuous cycle, 100% tolerant regenerants survived, though multiplication ability was decreased. After in vitro inoculation of the pathogen, seven out of eight somaclones exhibited tolerance to P. cactorum . Thus, it is suggested that selection approach using Phytophthora culture filtrate has potential in identifying the disease tolerant somaclones in apple.

中文翻译：

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苹果疫霉培养滤液体外筛选苹果砧木MM106体细胞克隆

使用最广泛的苹果砧木 Malling-Merton 106 对由 Phytophthora cactorum 引起的衣领腐烂病高度敏感。在本研究中，采用体外选择方法对 MM106 再生株的衣领腐烂耐受性进行早期筛选。将三个有毒的 P. cactorum 分离株产生的有毒滤液混合并作为选择剂进行测试。从 MM106 的叶外植体再生不定芽，克隆并暴露于富含 20-80% (v/v) 病原体培养滤液的增殖 MS 培养基中，以分离耐受再生体。不同浓度的培养滤液导致褐变、坏死和生长减少，从而导致耐受性芽的鉴定。存活的耐受性再生子经受三个连续和一个不连续选择循环。发现培养滤液的临界浓度为 74%，导致坏死后再生芽的存活率为 37.8%。在 70%、72% 和 74% 培养滤液富集培养基上选择的再生子在第二个选择周期后分别显示 52%、50% 和 33.3% 的存活率，而在第三个选择周期后分别降至 87%、81% 和 0。在不连续循环中，100% 耐受的再生体存活下来，但繁殖能力下降。在体外接种病原体后，八个体细胞克隆中有七个表现出对 P. cactorum 的耐受性。因此，建议使用疫霉属培养物滤液的选择方法在鉴定苹果中的抗病体细胞克隆方面具有潜力。在 70%、72% 和 74% 培养滤液富集培养基上选择的再生子在第二个选择周期后分别显示 52%、50% 和 33.3% 的存活率，而在第三个选择周期后分别降至 87%、81% 和 0。在不连续循环中，100% 耐受的再生体存活下来，但繁殖能力下降。在体外接种病原体后，八个体细胞克隆中有七个表现出对 P. cactorum 的耐受性。因此，建议使用疫霉属培养物滤液的选择方法在鉴定苹果中的抗病体细胞克隆方面具有潜力。在 70%、72% 和 74% 培养滤液富集培养基上选择的再生子在第二个选择周期后分别显示 52%、50% 和 33.3% 的存活率，而在第三个选择周期后分别降至 87%、81% 和 0。在不连续循环中，100% 耐受的再生体存活下来，但繁殖能力下降。在体外接种病原体后，八个体细胞克隆中有七个表现出对 P. cactorum 的耐受性。因此，建议使用疫霉属培养物滤液的选择方法在鉴定苹果中的抗病体细胞克隆方面具有潜力。虽然乘法能力下降。在体外接种病原体后，八个体细胞克隆中有七个表现出对 P. cactorum 的耐受性。因此，建议使用疫霉属培养物滤液的选择方法在鉴定苹果中的抗病体细胞克隆方面具有潜力。虽然乘法能力下降。在体外接种病原体后，八个体细胞克隆中有七个表现出对 P. cactorum 的耐受性。因此，建议使用疫霉属培养物滤液的选择方法在鉴定苹果中的抗病体细胞克隆方面具有潜力。