Damage to plants
Hi- it is probably a combination of factors including transplant shock (the plant getting used to outdoor conditions) and a small root system not yet able to fully mine the soil for water and nutrients.
Not really a problem if only lower and older leaves are affected. If the plant is receiving adequate sunlight, water, and nutrients, the top should be green and growing. You can prune off the lower leaf branches when the plant begins to produce fruit. This will improve air circulation resulting in faster leaf drying and reduced disease incidence.