What does hybrid vigor (heterosis) involve?

High levels of aspartic acid,low nitrogen and sugar content in maize plants prevent the attack by . . . . . . .

Explain the methods of breeding for disease resistance.

Match the columns:

Column-$I$	Column-$II$
$(a)$ Mustard	$(1)$ Pusa Sawani
$(b)$ Flat bean	$(2)$ Pusa Sadabahar
$(c)$ Okra	$(3)$ Pusa Gaurav
	$(4)$ Pusa Sem $2$

The host crop plants may be resistant to insect pests due to the
$I$. Morphological characteristics
$II$. Biochemical characteristics
$III$. Physiological characteristics
Choose the correct option.

Match the following columns:

Column-$I$	Column-$II$
$P$. Semi-dwarf varieties of wheat	$I$. Sonalika
$Q$. Semi-dwarf varieties of rice	$II$. $IR-8$
	$III$. Jaya
	$IV$. Kalyan Sona
	$V$. Taichung Native-$I$
	$VI$. Ratna