The mechanism of cross-protection, the deliberate infection of plants with a “mild” virus isolate to protect against “severe” isolates, has long been a topic of debate. In our model system, Citrus tristeza virus (CTV), this appears to be genotype-specific superinfection-exclusion, suggesting a simple recipe for cross-protection. However, this concept failed in field trials, which led us to examine the process of superinfection-exclusion more closely. We found that exclusion relies on the relative fitness of the primary versus the challenge isolates, and the host infected, and that significant differences in superinfection success could occur between isolates that differ by as few as 3 nucleotides. Furthermore, we found that exclusion was not uniform throughout the plant, but was tissue-specific. These data suggest that cross-protection is not a simple like-for-like process but a complex interaction between the primary and challenge isolates and the host.

交叉保护的机制，即用“轻度”病毒分离株故意感染植物以防止“重度”分离株，一直是争论的话题。在我们的模型系统中，柑桔三叶病毒（CTV），这似乎是特定于基因型的超级感染排除，这表明了进行交叉保护的简单方法。但是，这一概念在现场试验中失败了，这使我们更加仔细地研究了超感染-排斥的过程。我们发现，排斥依赖于主要菌株与攻击菌株以及感染宿主的相对适应性，并且在相差仅3个核苷酸的菌株之间可能会发生超级感染成功的显着差异。此外，我们发现排斥在整个植物中并不均匀，但具有组织特异性。这些数据表明，交叉保护不是一个简单的“按样进行”的过程，而是主要和挑战菌株与宿主之间复杂的相互作用。