Introduction
Guar (Cyamopsis tetragonoloba L.) is a highly important drought-tolerant legume crop with considerable potential for cultivation in arid and semi-arid regions. Beyond its intrinsic value as a food and forage crop, guar seed contains galactomannan gum, which is extensively utilized across the food, pharmaceutical, textile, paper, and oil industries. Expanding guar cultivation in water-limited environments like Sistan and Baluchestan Province, particularly the Saravan region, can significantly contribute to crop diversification and sustainable production systems. However, this region’s hot and dry climate, coupled with limited water resources and temperature fluctuations, strongly influences guar’s vegetative and reproductive growth phases. Planting date is a critical agronomic factor determining the environmental conditions experienced by the crop. Delayed planting often exposes reproductive stages to severe terminal drought and high temperatures. Native landraces, having evolved under specific environmental constraints, are valuable genetic resources that possess desirable traits for adaptation, earliness, and yield stability. Identifying the optimum planting date and the most adaptable native landrace is therefore essential for mitigating risks. Consequently, this study aimed to evaluate the interaction effects of planting dates and native landraces on guar phenology, yield components, and seed yield under Saravan’s climatic conditions.

Materials and Methods
The field experiment was conducted during the 2024–2025 cropping season in Saravan, Sistan and Baluchestan Province, Iran. A factorial experiment based on a randomized complete block design (RCBD) with three replications was implemented. The experimental factors comprised three planting dates (March 6, April 6, and May 5; corresponding approximately to 15 Esfand, 15 Farvardin, and 15 Ordibehesht) and three native guar landraces (Garmbit, Saravan, and Sarbaz). The experimental site featured a sandy loam soil with an electrical conductivity of 1.9 dS m⁻¹, a pH of 8.7, and 0.65% organic carbon. Soil total nitrogen was 0.07%, while available phosphorus and potassium were 12 and 210 mg kg⁻¹, respectively. Standard land preparation, including primary plowing, perpendicular disking, and leveling, was performed. Fertilization was applied based on soil test results, and all plots received uniform irrigation and standard agronomic management. Phenological traits, including vegetative and reproductive growth durations, were meticulously recorded. Furthermore, leaf area, number of pods per plant, number of seeds per pod, number of seeds per plant, 100-seed weight, and final seed yield (kg ha⁻¹) were evaluated. Data were subjected to analysis of variance, and treatment means were compared using appropriate mean comparison procedures to assess main and interaction effects.

Results and Discussion
The results demonstrated that planting date, landrace, and their interaction significantly affected all evaluated traits, including phenology, yield components, and final seed yield. This significant interaction implies that the native landraces exhibited distinct responses to planting date variations. The Sarbaz landrace displayed the highest yield potential under early planting conditions, producing a maximum seed yield of 2689 kg ha⁻¹ on March 6. This indicates its substantial genetic potential to exploit favorable early-season environmental conditions. However, its performance declined drastically under delayed planting. At the May 5 planting date, its seed yield dropped to 1033 kg ha⁻¹, representing a severe 62% reduction compared to early planting. This vulnerability was linked to the exposure of its critical reproductive stages to high terminal temperatures. In contrast, the Garmbit landrace exhibited exceptional yield stability across all planting dates. Its seed yield decreased from 2393 kg ha⁻¹ under the first planting date to 1535 kg ha⁻¹ under delayed planting, equating to a moderate reduction of only 36%. The superior stress tolerance of Garmbit was primarily attributed to its early maturity (ranging from 84 to 94 days), which facilitated a stress-escape strategy before the onset of severe late-season heat. Additionally, Garmbit successfully maintained an active photosynthetic source through a stable leaf area and preserved essential yield components, such as pod and seed production, under stress. Conversely, the Saravan landrace generally showed lower productivity and was more susceptible to terminal stress due to its later maturity.

Conclusion
The findings underscore the critical importance of matching planting dates with the specific genetic and phenological characteristics of guar landraces. The earliest planting date, March 6, provided the optimal environmental window for maximizing yield potential, particularly for the high-yielding but sensitive Sarbaz landrace. Thus, early planting of Sarbaz is strongly recommended when the goal is to achieve maximum productivity under favorable conditions. On the other hand, Garmbit was definitively identified as the most stable and adaptable landrace across varying planting dates. Its inherent early maturity, effective terminal stress-escape mechanism, and robust capacity to maintain leaf area and critical yield components minimized yield losses under delayed planting. Therefore, Garmbit is highly recommended for risk management, climate resilience, and sustainable guar production in Saravan and similar arid regions of Sistan and Baluchestan. Future breeding programs should continue to leverage these native genetic resources to enhance drought tolerance and yield stability.