Glossary: X-Y-Z

x
The letter ‘x’ is often used to indicate the basic chromosome number of a plant or species (e.g., x = 7). That is, ‘x’ is the number of chromosomes in a monoploid, or a single gamete.
If x = 7; then 2x = 14, and is a fertile diploid; 3x = 21, and is a sterile triploid; 4x = 28 and is a tetraploid which will be fully fertile if it is an allotetraploid; 5x = 35 and is a sterile pentaploid; and 6x = 42 and is a hexaploid that is likely to be sterile.
Xanthomonas
A genus of gram-negative bacteria that cause bacterial blights in beans, soybeans, cotton, rice, stone fruits, tomato, pepper, sugarcane, and various ornamentals.
Xanthosoma sagittifolium
Tannia, tannier, yautia, coco-yam. A typical aroid that differs from Colocasia in having sagittate leaves (i.e., leaves shaped like an arrow with an arrow-head), and in that it originated in the New World.
Xenia
Some visible characters of seeds, such as colour, shape, etc., can be induced by the pollen on either the maternal tissue or the embryo. This phenomenon is called xenia and it provides a useful means of identifying hybrids.
Xerophyte
A plant able to withstand drought.
Xylem
The woody tissues of a plant, consisting of microscopic water-conducting tubes, as well as thick lignified cells, which collectively provide strength to the stem. Timber consists largely of xylem.
Yam
See: Dioscorea spp.
Yautia
See: Xanthosoma sagittifolium.
Yield
The yield of a crop is usually expressed as weight per acre (or hectare). Yield is one of the four major objectives of plant breeding, the others being quality of crop product, agronomic suitability, and resistance to crop parasites.
Zea mais
The cereal known as ‘corn’ in the USA and Canada, and as maize in all other countries, and in all other languages. Maize is the third most important crop in the world. It is cross-pollinating and it exhibits strong inbreeding depression which permits the production of hybrid varieties.
Unlike wheat and rice, commercially grown maize is not normally consumed directly, and it is sent to factories for processing into many industrial products. It is also used as fodder, both as feed grains and silage. In subsistence farming, it is consumed directly by people.
Maize is a major staple (c.f., wheat and rice) that permitted the growth of cities in the New World. It also contributed to huge population increases in the Old World (c.f., beans, potatoes).
Zinc
Zinc is a trace element nutrient of plants. The deficiency symptoms show mainly as an interveinal chlorosis in the leaves which later become purple and necrotic.
Zingerberaceae
The botanical family that includes ginger, turmeric, and cardamom.
Zingiber officinale
Ginger, which probably originated in India and is of great antiquity in the Far East. It was also known to the Ancient Romans. The wild progenitors are extinct. The crop is propagated vegetatively and few clones are known. Flowering is rare, and this is a difficult crop to breed.
Zenia
The phenomenon in which plant tissues outside the embryo sac (i.e., edible fruit tissues) are influenced by the pollen. This phenomenon is seen, for example, with dates.
Zizania aquatica
Wild rice. Although a member of the grass family (Gramineae), it is not related to true rice.
Zygomorphic
An organism of irregular shape but which has two halves that are mirror images of each other. That is, the organism is divisible in only one plane into two mirror-image halves.
Zygote
A cell that was produced by the union of a male gamete and a female gamete.