1. A plant disease control composition comprising: (a): (a) a quinoline compound of general formula (I) of at least one species: [wherein R and R may be the same or different from each other and each represents: C- A C1-6 alkyl group which may be substituted with 1 to 3 identical or different substituents selected from the group consisting of a halogen atom, a C1-C6 alkoxy group, a C1-C6 alkylthio group and a phenoxy group, an aryl group which may be substituted with 1 to 6 identical or different substituents, selected from the group including a C 1 -C 6 alkyl group which may be substituted with 1 to 3 identical or different halogen atoms, a C 1 -C 6 alkoxy group, an amino group which may be substituted by 1 or 2 identical or different C 1 -C 6 alkyl groups or acyl groups, nitro group, cyano group , a mercapto group and a C 1 -C 6 alkylthio group, a heteroaryl group which may be substituted from 1 to 6 with the same or different substituents selected from the group consisting of a halogen atom, a C 1 -C 6 alkyl group which may be substituted with 1 to 3 identical or different atoms halogens, and a C1-C6 alkoxy group or an aralkyl group which may be substituted from 1 to 6 by the same or different substituents selected from the group consisting of a halogen atom, a C 1 -C 6 alkyl group which may be substituted with 1 to 3 identical or different halogen atoms, a C 1 -C 6 alkoxy group, an amino group which may be substituted with 1 or 2 identical or different C 1 -C 6 alkyl groups or acyl groups, nitro group, cyano group, hydroxyl group, mercapto group and C 1 -C 6 alkylthio group, or R 3 R a mercapto group and a C 1 -C 6 alkylthio group, a heteroaryl group which may be substituted from 1 to 6 with the same or different substituents selected from the group consisting of a halogen atom, a C 1 -C 6 alkyl group which may be substituted with 1 to 3 identical or different halogen atoms, and C1-C6 alkoxy group or an aralkyl group which may be substituted from 1 to 6 by the s
