The base of the silk is unique, as it elongates continuously until fertilization occurs. The cobs bear many rows of ovules that are always even in number. The female inflorescence or ear develops from one or more lateral branches shanks usually borne about half-way up the main stalk from auxiliary shoot buds.
As the internodes of the shanks are condensed, the ear remains permanently enclosed in a mantle of many husk leaves. Thus, the plant is unable to disperse its seeds in the manner of a wild plant and instead it depends upon human intervention for seed shelling and propagation.
Grain: The individual maize grain is botanically a caryopsis, a dry fruit containing a single seed fused to the inner tissues of the fruit case. The seed contains two sister structures, a germ which includes the plumule and radical from which a new plant will develop, and an endosperm which will provide nutrients for that germinating seedling until the seedling establishes sufficient leaf area to become autotrophy.
The endosperm of maize kernels can be yellow or white. Pollination occurs when these new moist silks catch the falling pollen grains. In maize, the pollen shed is not a continuous process and usually begins two to three days prior to silk emergence and continues for five to eight days. The silks are covered with fine, sticky hairs which serve to catch and anchor the pollen grains. Pollen shed stops when the tassel is too wet or too dry and begins again when temperature conditions are favorable.
Under favorable conditions, pollen grain remains viable for only 10 to 18 hours. Cool temperatures and high humidity favor pollen longevity.
Under optimal conditions the interval between anthesis and silking is one to two days. Type of corn. Corn variation may be artificially defined according to kernel type likes: dent, flint, flour, sweet, pop and pod corn etc.
Except for pod corn, these divisions are based on the quality, quantity and pattern of endosperm composition in the kernel and are not indicative of natural relationships Brown and Darrah, Dent Corn Dent corn is characterized by the presence of corneous, horny endosperm at the sides and back of the kernels, while the central core is a soft, floury endosperm extending to the crown of the endosperm.
It collapses to produce a distinct indentation on drying. Degree of denting varies with its genetic background. Dent corn is used primarily as animal food, but also serves as a raw material for industry and as staple food.
It is still an important human food and industrial material, entering into many specialized products via the dry- or wet-milling industry. However, white dent often receives a premium price in the dry milling industry, where it utilized for certain human food products because of its whiter starch.
Flint Corn The flint corns mostly have a thick, hard, vitreous glassy or corneous endosperm layer surrounded by small, soft granular center. The relative amounts of soft and corneous starch, however, vary in different varieties. Generally, the kernels are smooth and rounded, and the ears are long and slender with a comparatively small number of rows or kernels. In temperate zones, flint corn often matures earlier, germinates better has more spring vigor, more tillers and fewer prop roots than dent strains.
Flour Corn This is one of the oldest types of corn, tracing back to the ancient Aztecs and Incas. American and Indians used to ground the soft kernels for flour. Floury maize types have soft starch throughout, with practically no hard, vitreous endosperm and thus are opaque in kernel phenotype. Kernels tend to shrink uniformly upon drying, so usually have little or no denting. When dry, they are easy to grind, but may mold on the mature ear in wet areas.
The higher content of water-soluble polysaccharide adds a texture quality factor in addition to sweetness. Popcorn Popcorns are perhaps the most primitive of the surviving races of maize.
This corn type is characterized by a very hard, corneous endosperm containing only a small portion of soft starch. Popcorns are essentially small-kernelled flint types. The kernels may be either pointed rice-like or round pearl-like.
Some of the more recently developed popcorns have thick pericarps seed coats , while some primitive semi-popcorns, such as the Argentine popcorns, have thin pericarps. Pod Corn Pod corn tunicate maize is more of an ornamental type.
The major gene involved Tu produces long glumes enclosing each kernel individually, which also occurs in many other grasses. The ear is also enclosed in husks, as with other types of corn. Homozygous pod corn usually is highly self-sterile. Pod corn may be dent, sweet, waxy, pop, flint or floury in endosperm characteristics. It is merely a curiosity and is not grown commercially.
Waxy corn Waxy corn name derives from the waxy appearance of the endosperm exposed in a cleanly cut cross-section. Common corn starch is approximately 73 percent amylopectin and 27 percent amylose, whereas waxy starch is composed entirely with amylopectin, which is the branched molecular form of starch.
Ordinary corn starch stains blue with 2 percent potassium iodide solution, whereas waxy cornstarch stains a reddish brown. Totontepec is an indigenous agrarian community, and its land is held communally. Many residents are subsistence farmers who depend on the three crops of the milpa , the building blocks of indigenous agriculture in Mesoamerica: maize, squash, and beans.
Indigenous farmers domesticated landraces over millennia, carefully selecting and saving seeds for generations to meet their specific climatic and culinary needs. Bernal hosted Thomas Boone Hallberg and a group of scientists when they came to town in Ronald Ferrera-Cerrato, one of the scientists who went on the trip, is a microbiologist at the Postgraduate College Montecillo campus outside Mexico City. He tested the gel he brought back, finding evidence of nitrogen-fixing bacteria.
Metagenomics, the study of genetic material recovered from environmental samples, offered new possibilities to understand nitrogen fixation. Bennett had already begun collecting maize samples in in Totontepec under a simple material transfer agreement with the community.
Residents of Totontepec confirmed that the researchers frequently attended assemblies. But he participates in local government and attended assemblies where the scientists spoke. Even so, he was surprised to see the Nagoya Protocol certificate of compliance for the first time and wondered what it really meant for his community.
Bennett said that the U. Shapiro says it could take more than a decade for Mars or another company to breed the nitrogen-fixation trait into a commercial corn variety, if it is possible at all. Bennett says research continues at UC Davis to better understand and isolate the bacteria that fix nitrogen in the maize gel.
People familiar with the Totontepec case say it highlights some important shortcomings of the Nagoya Protocol, which went into effect in While the U. One is that Nagoya allows confidential agreements, despite transparency being a primary purpose of the protocol. For companies and universities, confidentiality is key to preventing their research from being copied. But for communities and advocates, it can prevent outside observers from assessing the fairness of the agreements between communities and multinational conglomerates.
Some countries, like Peru and South Africa, have taken steps toward more transparency, saying that when a company applies for a permit, the name of the species being accessed and the applicant must be made public.
An important issue in the Totontepec case is the decision by Mars Inc. That only Totontepec would receive compensation for the commercialization of a crop that is a regional natural resource strikes other communities and some outside observers as unjust.
When his contract with Mars was up at the end of , he did not renew it. Globally, about a billion tons of maize is produced per year. The history of maize is controversial, with scientists, historians and archaeologists proposing competing origin theories. One thing that is widely accepted is where maize comes from. Most scientists agree that maize originated in central Mexico and was domesticated , years ago from a wild grass called teosinte.
Teosinte looked nothing like modern maize, in particular due to its having smaller, fewer and more spaced out kernels, each surrounded by a tough casing. While it is descended from Teosinte, modern day corn, with its closely-packed kernels, does not exist in the wild and could not survive without human agricultural intervention. Early farmers in Mexico domesticated Teosinte by selecting the biggest and best kernels until the crop we recognise today as maize was arrived at.
Maize spread fast because it was nutritious, easy to grow, easy to store and easy to carry. Domesticated maize initially spread south down the coast to Peru and beyond, as well as across the North Americas, until eventually Native Americans continent-wide had adopted it as a vital part of their diet.
Before long, it was a staple food across most cultures in North and South America and the Caribbean. It was during this period that maize, along with three other crops that were subsequently to become vital staples in the Old World — potatoes, sweet potatoes and cassava — were brought to Europe. As well as these staples, a range of other foods came too, such as peanuts and pineapples and cocoa beans chilli peppers. La Santa Trinidad — a Spanish galleon. Earlier versions of such ships were used by the first European voyagers to reach the Americas.
0コメント