Crop load management in high density apple plantation

Aim of study: To optimize the best thinning method and elucidate its effect on fruit size, quality, yield and return bloom in apple under high density plantation in sub-temperate zone of India. Area of study: Dr. Yashwant Singh Parmar University of Horticulture and Forestry, Nauni, Solan, Himachal Pradesh, India. Material and methods: The experiment consisted of 30 combinations of 10 thinning (chemical and manual) treatments (T1: 10 mg L-1 NAA; T2: 20 mg L-1 NAA; T3: 100 mg L-1 BA; T4: 200 mg L-1 BA; T5: 100 mg L-1 Metamitron; T6: 200 mg L-1 Metamitron; T7: crop load of 4 fruits cm-2 TCSA; T8: crop load of 6 fruits cm-2 TCSA; T9: crop load of 8 fruits cm-2 TCSA and T10: control - no thinning) and 3 cultivars treatments (‘Jeromine’, ‘Redlum Gala’ and ‘Super Chief’), replicated five times over three growing seasons (2020 to 2022). Main results: The highest return bloom, fruit size, red skin color (RSC), sugars content, and anthocyanin content were produced due to manual thinning while maintaining a crop load of 4-6 fruits cm-2 TCSA (trunk cross sectional area). ‘Jeromine’ cultivar produced fruits with better yields, productivity, and RSC. ‘Redlum Gala’ had fruits with a better extent of thinning, return bloom, and sugar content. The extent of thinning showed a significant positive correlation with return bloom, fruit quality and physicochemical parameters, and growth in apples under high-density plantations. Research highlights: A possible threshold for optimal fruit quality and consistent return bloom is around 4-6 fruits cm-2 TCSA in apple under high density plantation in India.