Final answer:
The late blight disease cycle in potatoes starts with the infection of leaves by Phytophthora infestans and progresses as it destroys plant tissue and spreads through zoospore release, seriously impacting crop yields.
Step-by-step explanation:
The disease cycle of late blight in potatoes, caused by Phytophthora infestans, begins when the oomycete's hyphae infect a potato leaf, either through stomata or the cuticle. The organism quickly spreads throughout the leaf, causing cell death and the appearance of fruiting structures that release zoospores. These zoospores can swim through water films to infect additional plants. Late blight historically resulted in the Irish potato famine and continues to be a detrimental factor in potato agriculture, where it can destroy up to 70% of a crop without the use of pesticides.