Effect of Leaf Rust Disease on Berry Yield in Coffea liberica: A Two-Year Study of New Clonal Responses in MARDI Kluang, Malaysia

Coffee leaf rust (CLR), caused by the biotrophic fungus Hemileia vastatrix, is the most important coffee disease worldwide. Although Coffea liberica contributes less than 1% of global coffee production, it dominates Malaysia’s industry. However, information about how CLR affects Liberica yields under local field conditions is scarce. This study, therefore, assessed the effects of CLR on berry yield in five newly developed C. liberica clones under Malaysian field conditions. The study was carried out at the MARDI research station, Kluang, Johor, Malaysia, over two years (July 2021–June 2023). The experiment was arranged in a randomized complete block design with three replicates. Berry yield, disease incidence (INC) and disease severity index (DSI) were recorded monthly. Data were analyzed using ANOVA (Tukey’s test, p ≤ 0.05), and Pearson’s correlation was used to evaluate relationships between yield and disease parameters. Significant clonal variability was observed. Clone 213 consistently achieved the highest yields (1.420 kg/tree in Year 1; 0.623 kg/tree in Year 2) with the lowest disease levels (INC 27.2–19.4%; DSI 9.2–4.6%). Clone 222 was most susceptible, with the lowest yield and highest DSI, while clone 224 exhibited tolerance in Year 1 but declined sharply in Year 2. The control, MKL 7, produced moderate yields but was disease-sensitive. Yield–disease correlations were stronger in Year 2, reflecting biennial bearing and cumulative disease stress. The study, however, faced notable challenges. Biennial bearing complicated yield comparisons across years, as heavy fruiting inherently intensified disease severity. Seasonal climatic variability, including rainfall fluctuations and drought episodes, may also have confounded clonal responses. Furthermore, the two-year duration limits conclusions about long-term stability under changing environmental conditions. This study provides the first field-based evidence of CLR impacts on C. liberica yield in Malaysia. CLR substantially reduces productivity, but clone 213 emerges as a resistant, high-yielding candidate for sustainable cultivation.