Yōga Sūtra 2.04

अविद्या क्षेत्रमुत्तरेषां प्रसुप्ततनुविच्छिन्नोदाराणाम्।

avidyā kṣētramuttarēṣāṁ prasuptatanuvicchinnōdārāṇām।

[अविद्या क्षेत्रम् उत्तरेषां प्रसुप्त तनु विच्छिन्न उदाराणाम्।
avidyā = ignorance; kṣētram = is the ground; uttarēṣāṁ = breeding for; prasupta = that are dormant; tanu = weak; vicchinna = intermittent and; udārāṇām = active;]

Ignorance (avidya) is the breeding ground for other obstacles that are dormant, weak, intermittent, or fully active.

Out of the five obstacles, ignorance is the primary one as it is breeding ground for others.