Glossary Plant Breeding

Bt Genes. Genes (from the Gram Positive soil bacterium Bacillus thuringiensis)
encoding insecticidal crystal proteins (ICPs). ICPs are commonly designated “Cry”
proteins, and the genes encoding them are better known as “Cry” genes. Over fifty
such genes (Cry1Ac, Cry1C, Cry1B, Cry1D, and the like) have been identified and
sequenced. These are effective against caterpillars of Lepidopteran insects. The gene
has been incorporated in several crops including cotton. The gene product is a
crystalline protein, which remain in such plants in active form. When the insect
utilises such plants as its food, the crystalline protein causes paralysis of mid-gut, and
the insect ultimately dies.
Bt Crops. Genetically engineered crops known to carry stably integrated and expressed
Bt genes (Cry genes). Maize, rice, cotton and several other crops have been
genetically modified with Bt genes. These genes lead them to produce delta endotoxin
protein, which upon hydrolysis in alkaline environment of the mid-gut releases delta
endotoxins. These toxins through several intermediate reactions cause paralysis of the
digestivesystemsandleadtothedeathoftheinsect. Acottonvariety, BollGuard,
which is a product from a multinational company, is known to carry such a gene (Cry
1Ac). Apprehensions have been raised that the widespread cultivation of such crops
may cause intense selection pressure on the insects, and Bt genes are likely to be fixed
in the insect populations. Upon fixation, such crops will become ineffective as insectcontrol
agents. The second apprehension relates to exposure of human populations
continuously to such Bt-proteins.
Bud Sport. A somatic mutation expressed in a bud or branch of plants. Also called bud
mutation.
Bud Pollination. Placement of mature pollen on immature stigmas. This may allow
slow-growing incompatible pollen tube to reach ovary in time so that fertilization may
occur. The rationale is that stigma accumulates inhibitory biochemical substances
only if it gets matured. As temperature also plays an imortant role in the accumulation
of such inhibitory biochemicals, pollinating at low temerature may also accomplish
thesamepurpose.
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