Using a Stackelberg game model, this paper analyzes the problem of selecting downstream retailers for a fruit-producer who produces two kinds of fruits with partial substitutability under a joint-pricing strategy. There are two schemes for the fruit-producer wholesaling its fruits: one is wholesaling both of the fruits to one retailer, the other is wholesaling them to two different retailers separately. Through analyzing the two schemes under the wholesale-price and profit margin pricing strategy, it is concluded that, the fruit-producer's decisions of wholesale price remain the same in both schemes, while the retailers reduce their profit margin in the second scenario, which increases the total demand of the retail market and further stimulates the fruit-producer' investment, leading to an improvement in the fruit-producer's profit. Numerical results show that as the substitution rate of two fruits increases, the fruit producer will increase its wholesale prices to stimulate consumption, leading to an increase of the profit.