>Can you name examples of this "brittleness", how it is caused and how it has affected the food supply when compared to another way of farming
Not the parent but yes. Look at the history of banana cultivars. Up until the 1950s the most common variety of banana grown commercially was the 'Gros Michel'. Vast tracts of banana plantation of this single variety were wiped out by Panama disease which spread around the world. A different cultivar, the 'Cavendish' was found to be resistant to the strain of Panama disease that afflicted the Gros Michel. The transition was at great economic cost and it was fortuitous that a resistant variety of banana was discovered.
http://www.apsnet.org/publications/apsnetfeatures/Pages/Pana...
The first trades relied almost entirely on ‘Gros Michel’ (28,32). In many ways, ‘Gros Michel’ is an ideal export banana. It produces massive bunches of large, flavorful fruit that are so resistant to mechanical damage that they could be shipped intact. The downfall of ‘Gros Michel’ was its extreme susceptibility to Panama disease.
Panama disease was first reported in Australia, but became most important in the monocultures of ‘Gros Michel’ that were used by the trades in the Western Hemisphere. Panama was one of the first countries to experience major epidemics. It caused staggering losses in the trades before production areas converted to Cavendish. Between 1940 and 1960, 30,000 ha were lost in the Ulua Valley of Honduras, and in a decade complete losses were recorded in operations of 4,000 ha in Suriname and 6,000 ha in the Quepos area in Costa Rica. If one compiles figures up to 1960 and considers the substantial costs that were associated with plantation establishment, losses of approximately $400,000,000 can be attributed to Panama disease. Using a conservative conversion rate, this would be at least $2.3 billion in 2000 figures, and would be even greater if costs were included for unemployment, abandoned villages, unrealized income, and expenditures to maintain social stability in the affected regions.
I'm sure you can guess what happens next. A strain of Panama disease that affects the Cavendish has appeared:
http://www.apsnet.org/publications/apsnetfeatures/Pages/Pana...
The confidence that Panama disease would not affect the Cavendish clones was shattered in the early 1990s. New Cavendish plantations began to succumb throughout Southeast Asia, the home of banana. This represented the first time that Cavendish was affected in the tropics in the absence of predisposing factors.
The appearance of TR4 in Southeast Asia has changed this assessment. Once again the banana on which the export trades depend is threatened with destruction by Panama disease. Also affected are the important plantain cultivars that feed some 400 million people, as well as numerous cooking and dessert cultivars. In total, TR4 threatens more than 80% of the world’s banana production. Activities to monitor its spread and develop contingency plans for its arrival in other areas should be started as soon as possible.