According to Dr. James L. Brewbaker, the success of sustainable organic crop management in the tropics is dependent on breeding and research. While crops grown in temperate climates benefit from winter frosts that kill many pests and diseases, tropical crops, like corn, do not get such a break, and require a little help from science to thrive in northern climes. Conversely, crops bred to thrive in temperate climates are more susceptible to the ever-present and evolving viruses, pests and fungi in the tropics. Even crops like tomatoes, potatoes, peppers and eggplants, which were indigenous to the tropics, but were bred for the temperate climates in North America, now struggle when confronted by tropical diseases.
Brewbaker has spent more than 40 years breeding sweet corn at the University of Hawaii. He relies on conventional breeding methods, and on a technique called pyramiding, where he incorporates multiple genes for disease resistance in a single variety. In the early 1960s, Hawaii’s corn farmers dealt with a severe virus sickness problem. Today, Hawaii’s farmers are able to grow Brewbaker’s hybrid corn varieties pesticide-free.
Brewbaker and his colleagues continue striving to create improvements in corn, like getting a small tassel (male flower), which can expend a lot of the corn plant’s energy as it produces up to 10 million pollen cells for reproduction. Such reproductive effort is not necessary in modern agriculture, when large-scale commercial corn growers purchase new seed each year. Brewbaker describes the energy expended through the tassels as “a waste.” Scientists and growers hope most of the corn plant’s energy goes to the ear (female flower), which is the cash crop. Therefore, today’s corn hybrids are bred with as little “waste tissue” as possible; the idea is to create a big fat ear on a little skinny plant.
Brewbaker and his colleagues have found a gene that, in effect, cuts the size of the tassel in half. However, the tassel study will not immediately affect farmers. Brewbaker and other researchers will slowly change hybrids from big to small tassels, and it likely will increase yield less than 5 percent. Much greater impact comes from his research to create genetic improvements in disease resistance. The tassel mutation does not suggest anything about the health of the maize plant. “It has no effect, for example, on resistance to disease, insect, or ‘abiotic stress’ [i.e., lousy weather, bad soil, strange environment],” he explains. (After planting corn monthly for 350 of the past 400 months, Brewbaker has observed that an amazing and often unpredictable variation comes from genes interacting with environments.)
Brewbaker has also worked on breeding corn that resists tropical viruses and fungal diseases, focusing on diseases that have co-evolved with corn, such as rusts, blights and rots caused by fusarium fungi. Puccinia polysora, aka Southern rust, is a major disease in the warm tropics. This type of rust releases spores that have blown north from Mexico and the Caribbean and been found in fields in the southeastern U.S. during summer months. It only infects corn, but none of the country’s major corn types are resistant to it. Almost all American corns are highly susceptible, and it can literally kill. Brewbaker says if the disease evolved a more cold-tolerant race, the results could be disastrous. It is important to note that since Southern rust reproduces asexually, it is slow to evolve new races.
Rust was first serious in Africa in the 1950s, where it led to massive starvation. By the time Brewbaker started researching it in the late 1960s, the virus had spread to Thailand. The infection spread to Hawaii and Australia in the 1970s, but did not become serious in Hawaii until the early ’90s.
The evolution of new bacteria and fungi occurs very rapidly, leading to new races of diseases. Today, Brewbaker is working with Professor Jerald Pataky from the University of Illinois to identify races of Southern rust. In his breeding efforts, the scientist is careful to focus on “general” resistance, such as increasing durability and sustainability for all varieties of corn to all types of the above-mentioned diseases. Were he to focus on protecting one variety of corn from one specific race of disease, he would risk making his own work outdated and irrelevant before it was even finished, and ultimately helping no one. By working on a general level, for example in rust, Brewbaker has been able to help growers increase their yields by as much as 100 percent.
The author is a freelance writer based in Massachusetts and a monthly contributor to Growing.